Single controller for wearable sensor unit that includes an array of magnetometers

ABSTRACT

An exemplary magnetic field measurement system includes a wearable sensor unit and a single controller. The wearable sensor unit includes a plurality of magnetometers and a magnetic field generator configured to generate a compensation magnetic field configured to actively shield the magnetometers from ambient background magnetic fields. The single controller is configured to interface with the magnetometers and the magnetic field generator.

RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 62/842,818, filed on May 3, 2019, andto U.S. Provisional Patent Application No. 62/933,160, filed on Nov. 8,2019, and to U.S. Provisional Patent Application No. 62/933,167, filedon Nov. 8, 2019, and to U.S. Provisional Patent Application No.62/933,169, filed on Nov. 8, 2019, and to U.S. Provisional PatentApplication No. 62/933,170, filed on Nov. 8, 2019, and to U.S.Provisional Patent Application No. 62/933,287, filed on Nov. 8, 2019,and to U.S. Provisional Patent Application No. 62/933,288, filed on Nov.8, 2019, and to U.S. Provisional Patent Application No. 62/933,289,filed on Nov. 8, 2019, and to U.S. Provisional Patent Application No.62/933,174, filed on Nov. 8, 2019, and to U.S. Provisional PatentApplication No. 62/967,787, filed on Jan. 30, 2020, and to U.S.Provisional Patent Application No. 62/967,797, filed on Jan. 30, 2020,and to U.S. Provisional Patent Application No. 62/967,803, filed on Jan.30, 2020, and to U.S. Provisional Patent Application No. 62/967,804,filed on Jan. 30, 2020, and to U.S. Provisional Patent Application No.62/967,813, filed on Jan. 30, 2020, and to U.S. Provisional PatentApplication No. 62/967,818, filed on Jan. 30, 2020, and to U.S.Provisional Patent Application No. 62/967,823, filed on Jan. 30, 2020.These applications are incorporated herein by reference in theirrespective entireties.

BACKGROUND INFORMATION

Existing systems for observing or measuring weak magnetic fields (e.g.,magnetic fields generated by the brain) typically utilizeSuperconductive Quantum Interference Devices (SQUIDs) or opticalmagnetometry. SQUID systems require cryogenic cooling, which isprohibitively costly and bulky and requires a lot of maintenance, whichpreclude their use in mobile or wearable devices. Optical magnetometryuses optical methods to measure a magnetic field with very highaccuracy—on the order of 1×10⁻¹⁵ Tesla. Of particular interest for theirhigh-sensitivity, Optically Pumped Magnetometers (OPMs) have an alkalivapor gas cell that contains alkali metal atoms in a combination of gas,liquid, or solid states (depending on temperature). The gas cell maycontain a quenching gas, buffer gas, or specialized antirelaxationcoatings or any combination thereof. The size of the gas cells can varyfrom a fraction of a millimeter up to several centimeters.

Magnetoencephalography (MEG), the measurement of magnetic fieldsgenerated by the brain, and other types of magnetic field sensing may beperformed by a plurality of magnetometers (e.g., a collection ofdiscrete OPMs). A conventional magnetometer is controlled by a dedicatedcontroller, which has an independent clock used to drive variouscomponents within the magnetometer and receive signals from variouscomponents within the magnetometer. Accordingly, in a conventionalconfiguration that has an array of magnetometers, an array ofcontrollers (and hence an array of independent clocks) are used. Theclocks are not perfectly synchronized, which may lead to crosstalkbetween signals. This is disadvantageous for many reasons.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments and are a partof the specification. The illustrated embodiments are merely examplesand do not limit the scope of the disclosure. Throughout the drawings,identical or similar reference numbers designate identical or similarelements. Furthermore, the figures are not necessarily drawn to scale asone or more elements shown in the figures may be enlarged or resized tofacilitate recognition and discussion.

FIG. 1 illustrates an exemplary magnetic field measurement systemaccording to principles described herein.

FIG. 2 illustrates an exemplary computing device that may implement acontroller of the magnetic field measurement system of FIG. 1 accordingto principles described herein.

FIG. 3 illustrates an exemplary configuration of the magnetic fieldmeasurement system of FIG. 1 according to principles described herein.

FIG. 4 illustrates another exemplary configuration of the magnetic fieldmeasurement system of FIG. 1 according to principles described herein.

FIG. 5 illustrates yet another exemplary configuration of the magneticfield measurement system of FIG. 1 according to principles describedherein.

FIG. 6 illustrates a block diagram of an exemplary magnetometeraccording to principles described herein.

FIG. 7 shows a magnetic spectrum in magnetic field strength on alogarithmic scale according to principles described herein.

FIG. 8A illustrates an exemplary Bz′ component generator of a magneticfield generator according to principles described herein.

FIG. 8B illustrates an exemplary configuration of the Bz′ componentgenerator of FIG. 8A.

FIGS. 9A-9D illustrate exemplary functional diagrams of variousconfigurations of the Bz′ component generator of FIG. 8A according toprinciples described herein.

FIG. 10 illustrates another exemplary Bz′ component generator of amagnetic field generator according to principles described herein.

FIG. 11A illustrates a functional diagram of an exemplary configurationof the Bz′ component generator of FIG. 10 according to principlesdescribed herein.

FIG. 11B illustrates an exemplary configuration of the Bz′ componentgenerator 800 of FIGS. 10 and 11A according to principles describedherein.

FIG. 12 illustrates an exemplary functional diagram for driving a Bz′component generator according to principles described herein.

FIG. 13 illustrates another exemplary functional diagram for driving aBz′ component generator according to principles described herein.

FIGS. 14A and 14B show plan views of an exemplary Bx′/By′ componentgenerator according to principles described herein.

FIG. 14C shows a side view functional diagram of the Bx′/By′ componentgenerator of FIGS. 14A and 14B taken along the dashed lines labeledXIV-XIV according to principles described herein.

FIGS. 15A and 15B illustrate exemplary configurations of an elastomericconnector that may be used as interconnects in the Bx′/By′ componentgenerator of FIGS. 14A-14C according to principles described herein.

FIGS. 16A and 16B show plan views of another exemplary Bx′/By′ componentgenerator according to principles described herein.

FIG. 16C shows a side view functional diagram of the Bx′/By′ componentgenerator of FIGS. 16A and 16B taken along the dashed lines labeledXVI-XVI according to principles described herein.

FIGS. 17A and 17B show plan views of another exemplary Bx′/By′ componentgenerator according to principles described herein.

FIG. 17C shows a side view functional diagram of the Bx′/By′ componentgenerator of FIGS. 17A and 17B taken along the dashed lines labeledXVII-XVII according to principles described herein.

FIGS. 18A and 18B show plan views of an exemplary configuration of aBx′/By′ component generator according to principles described herein.

FIG. 18C shows a perspective view of various conductive windings thatmay be included in the Bx′/By′ component generator of FIGS. 18A and 18Baccording to principles described herein.

FIG. 19 shows an exemplary configuration in which a wearable sensor unit102 and a controller each include connection interfaces configured tofacilitate wired connections therebetween according to principlesdescribed herein.

FIG. 20 shows an exemplary configuration in which a controllerinterfaces with various components of or associated with a particularmagnetometer by way of a plurality of twisted pair cable interfacesaccording to principles described herein.

FIG. 21 shows another exemplary configuration in which a controllerinterfaces with various components of a particular magnetometer by wayof a plurality of twisted pair cable interfaces according to principlesdescribed herein.

FIG. 22 shows an exemplary configuration in which a controllerinterfaces with various components of a magnetic field generator by wayof a plurality of coaxial cable interfaces according to principlesdescribed herein.

FIG. 23 illustrates an exemplary configuration in which a controllerincludes a plurality of differential signal measurement circuitsaccording to principles described herein.

FIG. 24 shows an exemplary configuration in which a controller includescircuitry configured to measure current output by photodetectoraccording to principles described herein.

FIG. 25 shows exemplary circuitry that may be included in a controllerand used to supply a drive current to a heater included in a wearablesensor unit according to principles described herein.

FIG. 26 shows a perspective view of an exemplary physical implementationof a wearable sensor unit according to principles described herein.

FIG. 27 shows a cross sectional side view of the physical implementationof FIG. 26 according to principles described herein.

FIG. 28 shows an exemplary configuration in which a wearable sensor unitincludes a temperature control circuit according to principles describedherein.

FIG. 29 shows an exemplary configuration of a vapor cell according toprinciples described herein.

FIG. 30 shows an exemplary configuration in which a temperature controlcircuit creates a temperature gradient within a vapor cell according toprinciples described herein.

FIG. 31 illustrates another implementation of temperature controlcircuit according to principles described herein.

FIG. 32 is a perspective view of an exemplary implementation of atemperature control circuit according to principles described herein.

FIG. 33 illustrates a configuration in which a vapor cell includes areflecting element according to principles described herein.

FIGS. 34-39 illustrate embodiments of a wearable device that includeselements of wearable sensor units described herein according toprinciples described herein.

FIG. 40 illustrates an exemplary computing device according toprinciples described herein.

FIGS. 41-43 illustrate exemplary methods according to principlesdescribed herein.

DETAILED DESCRIPTION

Magnetic field measurement systems for use in MEG and/or otherapplications are described herein. For example, an exemplary magneticfield measurement system includes a wearable sensor unit and a singlecontroller. The wearable sensor unit includes a plurality ofmagnetometers and a magnetic field generator configured to generate acompensation magnetic field configured to actively shield themagnetometers from ambient background magnetic fields. The controller isconfigured to interface with the magnetometers and the magnetic fieldgenerator. For example, the controller may be configured to direct themagnetometers to detect magnetic fields generated within a user (e.g.,within a brain of the user) wearing the wearable sensor unit, controlvarious operating parameters of the magnetometers, and measure signalsoutput by the magnetometers. The controller may be further configured todirect the magnetic field generator to generate the compensationmagnetic field that actively shields the magnetometers from ambientbackground magnetic fields, control various operating parameters of themagnetic field generator, and measure various signals output by themagnetic field generator. These and other manners in which thecontroller may interface with the magnetometers and the magnetic fieldgenerator are described herein.

Advantageously, the controller uses a single common clock signal tocommunicate with the magnetometers and the magnetic field generator ofthe wearable sensor unit described herein. In this manner, thecontroller may ensure that communication with the magnetometers and themagnetic field generator is synchronized, thereby reducing oreliminating crosstalk between signals transmitted between the controllerand the wearable sensor unit. Moreover, use of a single controller (andtherefore a common clock signal) may result in more efficient andreliable communication between the controller and the wearable sensorunit compared to conventional configurations, less latency compared toconventional configurations, increased mobility of the wearable sensorunit compared to conventional configurations, and/or other benefits thatwill be made apparent herein.

FIG. 1 shows an exemplary magnetic field measurement system 100 (“system100”). As shown, system 100 includes a wearable sensor unit 102 and acontroller 104. Wearable sensor unit 102 includes a plurality ofmagnetometers 106-1 through 106-N (collectively “magnetometers 106”) anda magnetic field generator 108. Wearable sensor unit 102 may includeadditional components (e.g., one or more magnetic field sensors,position sensors, orientation sensors, accelerometers, image recorders,detectors, etc.) as may serve a particular implementation. System 100may be used in MEG and/or any other application that measures relativelyweak magnetic fields.

Wearable sensor unit 102 is configured to be worn by a user (e.g., on ahead of the user). In some examples, wearable sensor unit 102 isportable. In other words, wearable sensor unit 102 may be small andlight enough to be easily carried by a user and/or worn by the userwhile the user moves around and/or otherwise performs daily activities.

Any suitable number of magnetometers 106 may be included in wearablesensor unit 102. For example, wearable sensor unit 102 may include anarray of nine, sixteen, twenty-five, or any other suitable plurality ofmagnetometers 106 as may serve a particular implementation.

Magnetometers 106 may each be implemented by any suitable combination ofcomponents configured to be sensitive enough to detect a relatively weakmagnetic field (e.g., magnetic fields that come from the brain). Forexample, each magnetometer may include a light source, a vapor cell suchas an alkali metal vapor cell (the terms “cell”, “gas cell”, “vaporcell”, and “vapor gas cell” are used interchangeably herein), a heaterfor the vapor cell, and a photodetector (e.g., a signal photodiode).Examples of suitable light sources include, but are not limited to, adiode laser (such as a vertical-cavity surface-emitting laser (VCSEL),distributed Bragg reflector laser (DBR), or distributed feedback laser(DFB)), light-emitting diode (LED), lamp, or any other suitable lightsource. In some embodiments, the light source may include two lightsources: a pump light source and a probe light source. Thesemagnetometer components, and manners in which they operate to detectmagnetic fields, are described in more detail herein, as well as in inco-pending U.S. patent application Ser. No. 16/457,655, filed Jun. 28,2019, which application is incorporated by reference herein in itsentirety.

Magnetic field generator 108 may be implemented by one or morecomponents configured to generate one or more compensation magneticfields that actively shield magnetometers 106 (including respectivevapor cells) from ambient background magnetic fields (e.g., the Earth'smagnetic field, magnetic fields generated by nearby magnetic objectssuch as passing vehicles, electrical devices and/or other fieldgenerators within an environment of magnetometers 106, and/or magneticfields generated by other external sources). For example, magnetic fieldgenerator 108 may be configured to generate compensation magnetic fieldsin the Z direction, X direction, and/or Y direction (all directions arewith respect to one or more planes within which the magnetic fieldgenerator 108 is located). The compensation magnetic fields areconfigured to cancel out, or substantially reduce, ambient backgroundmagnetic fields in a magnetic field sensing region with minimal spatialvariability. As used herein, magnetic fields generated by magnetic fieldgenerator 108 in the Z direction are referred to as a Bz′ component ofthe compensation magnetic field, magnetic fields generated by magneticfield generator 108 in the X direction are referred to as a Bx′component of the compensation magnetic field, and magnetic fieldsgenerated by magnetic field generator 108 in the Y direction arereferred to as a By′ component of the compensation magnetic field.Specific implementations of magnetic field generator 108 are describedin more detail herein.

Controller 104 is configured to interface with (e.g., control anoperation of, receive signals from, etc.) magnetometers 106 and themagnetic field generator 108. Controller 104 may also interface withother components that may be included in wearable sensor unit 102.

In some examples, controller 104 is referred to herein as a “single”controller 104. This means that only one controller is used to interfacewith all of the components of wearable sensor unit 102. For example,controller 104 is the only controller that interfaces with magnetometers106 and magnetic field generator 108. This is in contrast toconventional configurations in which discrete magnetometers each havetheir own discrete controller associated therewith. It will berecognized, however, that any number of controllers may interface withcomponents of magnetic field measurement system 100 as may suit aparticular implementation.

As shown, controller 104 may be communicatively coupled to each ofmagnetometers 106 and magnetic field generator 108. For example, FIG. 1shows that controller 104 is communicatively coupled to magnetometer106-1 by way of communication link 110-1, to magnetometer 106-2 by wayof communication link 110-2, to magnetometer 106-N by way ofcommunication link 110-N, and to magnetic field generator 108 by way ofcommunication link 112. In this configuration, controller 104 mayinterface with magnetometers 106 by way of communication links 110-1through 110-N (collectively “communication links 110”) and with magneticfield generator 108 by way of communication link 112.

Communication links 110 and communication link 112 may be implemented byany suitable wired connection as may serve a particular implementation.For example, communication links 110 may be implemented by one or moretwisted pair cables while communication link 112 may be implemented byone or more coaxial cables. Advantages of such an implementation aredescribed in more detail herein. Other communication links betweencontroller 104 and wearable sensor unit 102 may additionally be includedto facilitate control of and/or communication with other componentsincluded in wearable sensor unit 102.

Controller 104 may be implemented in any suitable manner. For example,controller 104 may be implemented by a field-programmable gate array(FPGA), an application specific integrated circuit (ASIC), a digitalsignal processor (DSP), a microcontroller, and/or other suitable circuittogether with various control circuitry.

In some examples, controller 104 is implemented on one or more printedcircuit boards (PCBs) included in a single housing. In cases wherecontroller 104 is implemented on a PCB, the PCB may include variousconnection interfaces configured to facilitate communication links 110and 112. For example, the PCB may include one or more twisted pair cableconnection interfaces to which one or more twisted pair cables may beconnected (e.g., plugged into) and/or one or more coaxial cableconnection interfaces to which one or more coaxial cables may beconnected (e.g., plugged into).

In some examples, controller 104 may be implemented by or within acomputing device. FIG. 2 illustrates an exemplary computing device 200that may implement controller 104. Computing device 200 may beimplemented by a desktop computer, a mobile device, a server, and/or anyother single computing device having a single housing for components ofthe computing device.

As shown, computing device 200 may include, without limitation, astorage facility 202 and a processing facility 204 selectively andcommunicatively coupled to one another. Facilities 202 and 204 may eachinclude or be implemented by hardware and/or software components (e.g.,processors, memories, communication interfaces, instructions stored inmemory for execution by the processors, etc.).

Storage facility 202 may maintain (e.g., store) executable data used byprocessing facility 204 to perform one or more of the operationsdescribed herein. For example, storage facility 202 may storeinstructions 206 that may be executed by processing facility 204 toperform one or more of the operations described herein. Instructions 206may be implemented by any suitable application, software, code, and/orother executable data instance. Storage facility 202 may also maintainany data received, generated, managed, used, and/or transmitted byprocessing facility 204.

Processing facility 204 may be configured to perform (e.g., executeinstructions 206 stored in storage facility 202 to perform) variousoperations described herein.

As shown, computing device 200 may be communicatively coupled to a userinput device 208 and to a display device 210. User input device 208 maybe implemented by a keyboard, a mouse, a touch screen, a track ball, ajoystick, a voice recognition system, and/or any other componentconfigured to facilitate providing of user input to computing device200. Display device 210 may be implemented by a monitor, a screen, aprinter, and/or any other device configured to display output providedby computing device 200. In some examples, display device 210 isintegrated into a single unit with computing device 200.

FIG. 3 illustrates an exemplary configuration 300 of system 100 in whichcontroller 104 includes a clock source 302 configured to generate acommon clock signal used by controller 104 to interface with thecomponents of wearable sensor unit 102. For example, controller 104 mayuse the common clock signal to drive or otherwise control variouscomponents within each of magnetometers 106 and drive or otherwisecontrol magnetic field generator 108. Use of the common clock signal tointerface with magnetometers 106 and magnetic field generator 108 isillustrated in FIG. 3 (and various other figures) by dashed linesinterconnecting clock source 302 and magnetometers 106 and magneticfield generator 108.

By using a single common clock signal (as opposed to an array ofindependent clocks as done in conventional configurations), controller104 may ensure that communication with magnetometers 106 and magneticfield generator 108 (and, in some implementations, other componentswithin wearable sensor unit 102) is synchronized, thereby reducing oreliminating crosstalk between signals transmitted between controller 104and wearable sensor unit 102, as well as providing other benefitsdescribed herein.

In some implementations, as illustrated in FIGS. 1 and 3, controller 104is remote from (i.e., not included within) wearable sensor unit 102. Forexample, in these implementations, controller 104 may be implemented byor included in a standalone computing device not configured to be wornby a user (e.g., computing device 200). The computing device mayinterface with one or more user input devices (e.g., user input device208) and one or more display devices (e.g., display device 210). In thismanner, a user may provide user input by way of the computing device tocontrol, program, configure, and/or otherwise interface with controller104. The computing device may present information (e.g., output datagenerated by wearable sensor unit 102) by way of the one or more displaydevices.

FIG. 4 shows an alternative configuration 400 in which controller 104 isincluded within wearable sensor unit 102. Configuration 400 may allow auser of wearable sensor unit 102 to travel or otherwise move freelywhile still wearing wearable sensor unit 102 without having to ensurethat wearable sensor unit 102 is connected to a separate non-wearablecontroller.

In configuration 400, controller 104 may include one or more interfaces(e.g., wired or wireless interfaces) configured to facilitatecommunication between controller 104 and an external computing device.In this manner, a user may use the external computing device to control,program, configure, or otherwise interface with controller 104. Wearablesensor unit 102 may further include a power supply (not shown)configured to provide operating power to controller 104 and variousother components included in wearable sensor unit 102.

As another exemplary configuration, controller 104 may be included in awearable sensor unit other than wearable sensor unit 102. For example, amagnetic field measurement system may include a first wearable sensorunit and a second wearable sensor unit. A controller included in thefirst wearable sensor unit may be communicatively coupled to the secondwearable sensor unit and configured to control both the first and secondwearable sensor units. To this end, the first and second wearable sensorunits may be communicatively coupled by way of any suitablecommunication link.

As another exemplary configuration, controller 104 may be included in awearable device configured to be worn by a user and separate fromwearable sensor unit 102. For example, controller 104 may be included ina wearable device (e.g., a device that may be worn on the head, on theback (e.g., in a backpack), and/or on the waist (e.g., in a unitconfigured to clip or strap to a belt of the user) and communicativelycoupled to wearable sensor unit 102 by way of any suitable communicationlink. Examples of this are described herein.

FIG. 5 shows an exemplary configuration 500 in which controller 104 isconfigured to concurrently interface with multiple wearable sensor units(e.g., multiple wearable sensor units configured to be worn concurrentlyby a user). For example, as shown, controller 104 is communicativelycoupled to wearable sensor unit 102-1 and wearable sensor unit 102-2(collectively “wearable sensor units 102”). As shown, both wearablesensor units 102 include a plurality of magnetometers 106 and a magneticfield generator 108. As shown, controller 104 may interface withmagnetometers 106 by way of communication links 110 and with magneticfield generators 108 by way of communication links 112.

As shown, the common clock signal output by clock source 202 isconfigured to be used by controller 104 to control or otherwiseinterface with all of the components of both wearable sensor units 102.In this manner, operation of and data output by wearable sensor units102 may be synchronized.

In the examples described above, controller 104 of system 100 maycontrol or interface with various components of one or more wearablesensor units 102 to measure biological or other magnetic fields. Asexplained above, a wearable sensor unit 102 may include, in someexamples, one or more magnetometers 106 and a magnetic field generator108. These components will now be described.

Magnetometers 106 may be any suitable magnetometers, such as but notlimited to optically pumped magnetometers (OPMs), nitrogen vacancy (NV)diamond sensors, and magnetoresistance sensors. OPMs may operate in avector mode and/or a scalar mode. In some examples, vector mode OPMs mayoperate at zero-fields and may utilize a spin exchange relaxation free(SERF) mode to reach femto-Tesla sensitivities.

FIG. 6 illustrates a block diagram of an exemplary magnetometer 106. Asshown, magnetometer 106 is an OPM. Magnetometer 106 includes a lightsource 602, a vapor cell 604, a signal photodetector 606, and a heater608. In addition, the magnetic field generator 108 can be positionedaround the vapor cell 604. Magnetometer 106 may include additional oralternative components as may suit a particular implementation, such asoptics (e.g., lenses, waveplates, collimators, polarizers, and/orobjects with reflective surfaces for beam shaping and polarizationcontrol and for directing light from light source 602 to vapor cell 604and to signal photodetector 606) and/or any other suitable components.

Light source 602 is configured to generate and emit light (e.g., laserlight) to optically pump alkali metal atoms in vapor cell 604 and toprobe vapor cell 604. Examples of suitable light source devices include,but are not limited to, a diode laser (e.g., a vertical-cavitysurface-emitting laser (VCSEL), a distributed Bragg reflector laser(DBR), a distributed feedback laser (DFB), etc.), a light-emitting diode(LED), a lamp, or any other suitable light source.

Vapor cell 604 contains an alkali metal vapor (e.g., rubidium in naturalabundance, isotopically enriched rubidium, potassium, or cesium, or anyother suitable alkali metal such as lithium, sodium, potassium,rubidium, cesium, or francium) and, optionally, a quenching gas (e.g.,nitrogen) and/or a buffer gas (e.g., nitrogen, helium, neon, or argon).It will be recognized that vapor cell 604 can contain additional orother gases or vapors as may suit a particular implementation. Heater608 is configured to heat vapor cell 604.

Signal photodetector 606 is configured to detect and measure opticalproperties (e.g., amplitude, phase, and/or polarization) of lightemitted by light source 602 that has passed through vapor cell 604.Examples of suitable signal photodetectors include, but are not limitedto, a photodiode, a charge coupled device (CCD) array, a CMOS array, acamera, a photodiode array, a single photon avalanche diode (SPAD)array, an avalanche photodiode (APD) array, and/or any other suitableoptical sensor array that can measure a change in transmitted light atthe optical wavelengths of interest.

Operation of magnetometer 106 will now be described. Light emitted bylight source 602 enters vapor cell 604 where it induces a transparentsteady state in the alkali metal vapor. In the transparent steady statethe light is allowed to pass through the vapor cell 604 with minimalabsorption by the alkali metal vapor and, hence, maximal detection bysignal photodetector 606. Magnetic fields generated from a target source(e.g., magnetic fields generated by a user's brain) cause thetransparency of the alkali metal vapor to decrease so that less light isdetected at signal photodetector 606. The change in light detected atsignal photodetector 606 is correlated to magnetic fields generated bythe target source.

However, ambient background magnetic fields may interfere with themeasurement by magnetometer 106 of magnetic fields generated by a targetsource. As used herein, the term “ambient background magnetic fields”refers to a magnetic field or magnetic fields associated with (e.g.,generated by) sources other than system 100 and the sources of interest(e.g., magnetic fields associated with neural signals from a user'sbrain). The ambient background magnetic fields can include, for example,the Earth's magnetic field as well as magnetic fields from magnets,electromagnets, electrical devices, and other signal or field generatorsin the environment other than magnetic field generator 108 that is partof system 100.

FIG. 7 shows the magnetic spectrum from 1 fT to 100 μT in magnetic fieldstrength on a logarithmic scale. The magnitude of magnetic fieldsgenerated by the human brain are indicated by range 702 and themagnitude of ambient background magnetic fields, including the Earth'smagnetic field, by range 704. The strength of the Earth's magnetic fieldcovers a range as it depends on the position on the Earth as well as thematerials of the surrounding environment where the magnetic field ismeasured. Range 706 indicates the approximate measurement range of amagnetometer (e.g., an OPM) operating in the SERF mode (e.g., a SERFmagnetometer) and range 708 indicates the approximate measurement rangeof a magnetometer operating in the scalar mode (e.g., a scalarmagnetometer.) Typically, a SERF magnetometer is more sensitive than ascalar magnetometer, but many conventional SERF magnetometers typicallyonly operate up to about 0 to 200 nT while the scalar magnetometerstarts in the 10 to 100 fT range but extends above 10 to 100 μT. At veryhigh magnetic fields the scalar magnetometer typically becomes nonlineardue to a nonlinear Zeeman splitting of atomic energy levels.

As can be seen from FIG. 7, SERF magnetometers have high sensitivitybut, conventionally, cannot function in a magnetic field higher thanabout 50 nT, which is approximately 1/1000 of the magnetic fieldstrength generated by the Earth. For a SERF magnetometer to accuratelymeasure biological and other weak signals, the strength of ambientbackground magnetic fields, including the Earth's magnetic field, needto be canceled or reduced to at least less than about 10-20 nT.Accordingly, wearable sensor unit 102 includes one or more activemagnetic field shields (e.g., magnetic field generator 108) and,optionally, one or more passive magnetic field shields. An activemagnetic field shield generates, for example, an equal and oppositemagnetic vector that cancels out, or substantially reduces, the ambientbackground magnetic fields. A passive magnetic field shield redirectsmagnetic fields away from magnetic field sensors (e.g., away frommagnetometers 106). Exemplary passive magnetic field shields aredescribed in more detail in U.S. patent application Ser. No. 16/457,655,which is incorporated herein by reference in its entirety.

Magnetic field generator 108 is configured to generate a compensationmagnetic field configured to actively shield a magnetic field sensingregion from ambient background magnetic fields. An ambient backgroundmagnetic field B is a vector magnetic field that has magnitude anddirection at each point in space. Using the Cartesian coordinate system,ambient background magnetic field B can be expressed as:B=i·Bx+j·By+k·Bzwhere Bx, By and Bz are the Cartesian components of the ambientbackground magnetic field and i, j, and k are unit vectors along the x-,y-, and z-axes. The compensation magnetic field B′ generated by magneticfield generator 108 is expressed as:B′=i·Bx′+j·By′+k·Bz′where Bx′, By′ and Bz′ are the Cartesian components of the compensationmagnetic field and i, j, and k are unit vectors along the x-, y-, andz-axes. In some examples, controller 104 may determine the compensationmagnetic field to be generated by magnetic field generator 108. Forexample, controller 104 may interface with one or more magnetic fieldsensors included in wearable sensor unit 102 to measure the ambientbackground magnetic field B. Controller 104 may determine thecompensation magnetic field B′ (e.g., determine the Bx′ component, theBy′ component, and/or the Bz′ component of compensation magnetic fieldB′) based on the measured ambient background magnetic field B. Exemplarymethods for determining a compensation magnetic field are described indetail in U.S. patent application Ser. No. 16/213,980, which isincorporated by reference herein in its entirety. Controller 104 maythen drive magnetic field generator 108 to generate the compensationmagnetic field.

The compensation magnetic field generated by magnetic field generator108 may actively shield the magnetic field sensing region by cancelingor substantially reducing (e.g., by at least 80%, 85%, 90%, 95%, or 99%,etc.) ambient background magnetic fields in one, two, or threedimensions. For example, magnetic field generator 108 may include one ormore of a Bz′ component generator, a Bx′ component generator, and/or aBy′ component generator configured to cancel or substantially reduceambient background magnetic fields along a z-axis, an x-axis, and/or ay-axis associated with magnetic field generator 108.

FIG. 8A illustrates an exemplary Bz′ component generator 800 of magneticfield generator 108. As shown, Bz′ component generator 800 includes aplurality of conductive windings 802 arranged in opposing parallelplanes. For example, Bz′ component generator 800 includes a firstconductive winding 802-1 arranged in a first plane and a secondconductive winding 802-2 arranged in a second plane that issubstantially parallel to the first plane. A magnetic field sensingregion 804 is located between conductive winding 802-1 and conductivewinding 802-2. Magnetic field sensing region 804 is a region where oneor more magnetometers 106 (e.g., vapor cells 604) may be located.

Bz′ component generator 800 is configured to actively shield magneticfield sensing region 804 (and hence magnetometers 106) from ambientbackground magnetic fields along a z-axis, such as by substantiallyreducing or canceling a Bz component of ambient background magneticfields at magnetic field sensing region 804. Legend 806 indicates anorientation of x-, y-, and z-axes, which have been arbitrarily assignedrelative to components of magnetic field generator 108. As indicated bylegend 806, the z-axis is a direction normal to the first plane and thesecond plane, the x-axis is a direction orthogonal to the z-axis andparallel to the first plane and the second plane, and the y-axis is adirection orthogonal to the z-axis and the x-axis and parallel to thefirst plane and the second plane.

Each conductive winding 802 comprises one or more coils, half coils,loops, and/or turns of conductive wiring forming a continuous electricalpath arranged substantially in a single plane. Conductive windings 802may be formed of any suitable conductor of electrical current, such asmetallic conductors (e.g., copper, silver, and/or gold) and non-metallicconductors (e.g., carbon). Each conductive winding 802 may be arrangedin a plane in any suitable way. In some examples, each conductivewinding 802 is arranged (e.g., etched, printed, soldered, deposited, orotherwise attached) on a planar substrate. The planar substrate may beformed of any suitable material, such as but not limited to alumina,ceramics, glass, and/or PCB material. FIG. 8B illustrates an exemplaryconfiguration of Bz′ component generator 800 in which conductive winding802-1 is arranged on an upper surface of a first PCB 808-1 andconductive winding 802-2 (not shown) is arranged on a bottom surface ofa second PCB 808-2. Second PCB 808-2 is substantially parallel to firstPCB 808-1. While PCBs 808 are shown to be round, they may be any othershape as may suit a particular implementation. PCBs 808 may be supportedand maintained in substantially parallel alignment in any suitable way,such as by one or more posts, screws, or other suitable supportingstructures.

FIGS. 9A-9D show exemplary functional diagrams of Bz′ componentgenerator 800 and illustrate various configurations in which conductivewindings 802 may be arranged on parallel planes. In FIGS. 9A-9Dconductive windings 802 are shown to have a vertical (z-direction)dimension above substrates 902 on which they are arranged. However, thisis only for illustration purposes, as conductive windings 802 may beimplemented by traces on substrates 902 or otherwise be embedded withinsubstrates 902.

FIG. 9A illustrates an exemplary configuration in which Bz′ componentgenerator 800 includes a single substrate 902. Conductive winding 802-1is arranged on a first surface 904-1 of substrate 902 and conductivewinding 802-2 is arranged on a second surface 904-2 of substrate 902.First surface 904-1 corresponds to the first plane and second surface904-2 corresponds to the second plane. Substrate 902 has a hole 906aligned with center openings of conductive windings 802. Magnetic fieldsensing region 804 is located in hole 906.

FIG. 9B illustrates another exemplary configuration in which Bz′component generator 800 includes two substrates 902 (e.g., firstsubstrate 902-1 and second substrate 902-2). Conductive winding 802-1 isarranged on an outer surface 904-1 of first substrate 902-1 (e.g., asurface facing away from magnetic field sensing region 804) andconductive winding 802-2 is arranged on an outer surface 904-2 of secondsubstrate 902-2 (e.g., a surface facing away from magnetic field sensingregion 804). Outer surface 904-1 corresponds to the first plane andouter surface 904-2 corresponds to the second plane.

FIG. 9C illustrates another exemplary configuration of Bz′ componentgenerator 800. FIG. 9C is the same as FIG. 9B except that conductivewinding 802-1 is arranged on an inner surface 904-3 of first substrate902-1 (e.g., a surface facing magnetic field sensing region 804) andconductive winding 802-2 is arranged on an inner surface 904-4 of secondsubstrate 902-2 (e.g., a surface facing magnetic field sensing region804). Inner surface 904-3 corresponds to the first plane and innersurface 904-4 corresponds to the second plane.

FIG. 9D illustrates another exemplary configuration of Bz′ componentgenerator 800. FIG. 9D is the same as FIG. 9B except that conductivewinding 802-1 is arranged on inner surface 904-3 of first substrate902-1 (e.g., a surface facing magnetic field sensing region 804), whileconductive winding 802-2 is arranged on outer surface 904-2 of secondsubstrate 902-2 (e.g., a surface facing away from magnetic field sensingregion 804). Inner surface 904-3 corresponds to the first plane andouter surface 904-2 corresponds to the second plane.

In the foregoing examples, Bz′ component generator 800 has twoconductive windings. However, Bz′ component generator 800 may have anyother number of conductive windings as may suit a particularimplementation, as illustrated in FIG. 10. FIG. 10 is the same as FIG.8A except that the plurality of conductive windings 802 further includesa conductive winding 802-3 arranged in a third plane and a conductivewinding 802-4 arranged in a fourth plane. The third plane and the fourthplane are substantially parallel to the first plane and the secondplane. Magnetic field sensing region 804 is located between conductivewindings 802-3 and 802-4. However, magnetic field sensing region 804 maybe located in any other suitable location.

Conductive windings 802-3 and 802-4 may be arranged on the third planeand the fourth plane in any manner described herein. FIG. 11A shows afunctional diagram of another exemplary configuration of Bz′ componentgenerator 800. FIG. 11A is the same as FIG. 9B except that conductivewinding 802-3 is arranged on inner surface 904-3 of first substrate902-1 and conductive winding 802-4 is arranged on inner surface 904-4 ofsecond substrate 902-2. Inner surface 904-3 corresponds to the thirdplane and inner surface 904-4 corresponds to the fourth plane. FIG. 11Billustrates an exemplary configuration of Bz′ component generator 800shown in FIGS. 10 and 11A. FIG. 11B is the same as FIG. 8B except thatconductive winding 802-3 (not visible in FIG. 11B) is arranged on aninner surface of first PCB 808-1 (e.g., a surface facing magnetic fieldsensing region 804) and conductive winding 802-4 is arranged on an innersurface of second PCB 808-2 (e.g., a surface facing magnetic fieldsensing region 804).

The foregoing examples show conductive windings 802-1 through 802-4arranged on two substrates (e.g., PCBs 808 or substrates 902). In otherexamples conductive windings 802-1 through 802-4 may be arranged on morethan two substrates. For instance, each conductive winding 802 may eachbe arranged on a separate substrate. However, arranging multipleconductive windings 802 on a single substrate (e.g., on oppositesurfaces of a substrate, as illustrated in FIGS. 11A and 11B) fixes thealignment of the conductive windings 802 relative to one another andthus prevents inadvertent misalignments.

In the examples described above, conductive windings 802 may have anywinding pattern as may suit a particular implementation. As used herein,a winding pattern may refer to the path of conductive wiring, thespacing between adjacent wires, a width/thickness of wires, the numberof loops or turns, the direction of current flow, and the like. In someexamples the winding patterns of conductive windings 802 may beautomatically generated by a magnetic field generator design systemconfigured to optimize the winding patterns based on a set of inputs. Anexemplary magnetic field generator design system will be described belowin more detail. Generally, the winding patterns of conductive windings802 are configured to generate a homogeneous magnetic field at themagnetic field sensing region. The winding patterns may be configured togenerate a homogeneous magnetic field that is approximately 30% the sizeof conductive windings 802, as measured along the x- or y-direction.

In some examples, winding patterns of the plurality of conductivewindings are substantially identical (e.g., mirror images of oneanother). For example, conductive winding 802-1 may be substantiallyidentical to conductive winding 802-2. Additionally, conductive windings802-3 and 802-4 may be substantially identical to each other and/or toconductive windings 802-1 and 802-2.

In some examples, conductive windings 802 may grouped into pairs (e.g.,based on a drive current supplied, a location of conductive windings802, etc.) such that conductive windings 802 within a particular pairhave the same winding patterns, but different pairs of conductivewindings 802 have different winding patterns. For instance, windingpatterns of conductive windings 802-1 and 802-2 may be substantiallyidentical, and winding patterns of conductive windings 802-3 and 802-4may be substantially identical but different from the winding patternsof conductive windings 802-1 and 802-2.

In some examples, conductive windings 802 within a particular pair ofconductive windings have different winding patterns. For instance,winding patterns of conductive windings 802-1 and 802-2 may be differentfrom one another. This may be desirable when magnetic sensing region 804is off-center in the z-direction (e.g., is closer to first substrate902-1 or second substrate 902-2). Winding patterns of conductivewindings 802-3 and 802-4 may be substantially identical or may also bedifferent from one another.

Controller 104 is configured is to drive conductive windings 802 bysupplying one or more drive currents to conductive windings 802. FIG. 12shows an exemplary functional diagram indicating how controller 104 maydrive Bz′ component generator 800. As shown, controller 104 may supply afirst drive current 1202-1 to conductive winding 802-1 and supply asecond drive current 1202-2 to conductive winding 802-2. Drive currents1302 may be supplied, for example, by way of communication link 112.

FIG. 13 illustrates another exemplary schematic illustrating howcontroller 104 may drive Bz′ component generator 800. FIG. 13 is thesame as FIG. 12 except that Bz′ component generator 800 further includesconductive windings 802-3 and 802-4. Accordingly, controller 104 isconfigured to supply a third drive current 1202-3 to conductive winding802-3 and supply a fourth drive current 1202-4 to conductive winding802-4. Drive currents 1202-3 and 1202-4 may be supplied by way ofcommunication link 112.

Conductive windings 802 are configured to generate a Bz′ component of acompensation magnetic field when conductive windings 802 are suppliedwith drive currents 1202. The Bz′ component of the compensation magneticfield is configured to actively shield magnetic field sensing region 804from ambient background magnetic fields along the z-axis, such as byreducing or canceling a Bz component of ambient background magneticfields. In some examples, the Bz′ component of the compensation magneticfield is substantially equal and opposite to the Bz component of theambient background magnetic fields.

Controller 104 may drive conductive windings 802 in any suitable way.For example, controller 104 may supply conductive windings 802 with thesame drive current 1202. In other words, drive currents 1202 may all bethe same current. In some examples controller 104 includes a singledriver configured to supply all drive currents 1202 to conductivewindings 802. In alternative examples, controller 104 includes aplurality of individual drivers each configured to supply a drivecurrent 1202, but controller 104 controls the drivers to supply the samedrive current to conductive windings 802. By driving conductive windings802 such that drive currents 1202 are the same, conductive windings 802generate a uniform magnetic field along the z-direction in magneticfield sensing region 804.

Alternatively to supplying conductive windings 802 with the same drivecurrent, controller 104 may supply one or more of conductive windings802 with a drive current that is different from drive currents suppliedto other conductive windings 802. For example, drive current 1202-1 maybe different from drive current 1202-2. Additionally or alternatively,drive current 1202-3 may be different from drive current 1202-4. Whenconductive windings 802-1 and 802-2 are driven with different drivecurrents, Bz′ component generator 800 generates a gradient magneticfield (e.g., a dBz′/dz gradient). When conductive windings 802-1 and802-2 are driven with different drive currents and conductive windings802-3 and 802-4 are driven with the same drive (or vice versa), Bz′component generator 800 generates a gradient magnetic field in additionto the Bz′ component of the compensation magnetic field. The gradientmagnetic field is configured to actively shield magnetic field sensingregion from fields that linearly vary along the z-axis, as will beexplained below in more detail.

As mentioned above, magnetic field generator 108 may include, inaddition to or in place of Bz′ component generator 800, a Bx′ componentgenerator and/or a By′ component generator configured to cancel orsubstantially reduce ambient background magnetic fields along the x-axisand/or the y-axis.

FIGS. 14A-14C illustrate an exemplary configuration of a Bx′/By′component generator 1400 of magnetic field generator 108. FIGS. 14A and14B show plan views (e.g., views in the z-direction) of Bx′/By′component generator 1400, and FIG. 14C is a side view functional diagramof Bx′/By′ component generator 1400 (e.g., as viewed in the y-direction)taken along the dashed lines labeled XIV-XIV. Legend 1402 indicates anorientation of x-, y-, and z-axes. The orientation of legend 1402 is thesame as the orientation of legend 806 relative to magnetic fieldgenerator 108.

As shown, Bx′/By′ component generator 1400 includes a first substrate1404-1 and a second substrate 1404-2 positioned opposite to firstsubstrate 1404-1 and separated from first substrate 1404-1 in thez-direction by a gap. Substrates 1404 may be formed of any suitablematerial, such as but not limited to alumina, ceramics, glass, and/orPCB board. In some examples in which magnetic field generator 108includes Bx′/By′ component generator 1400 in addition to Bz′ componentgenerator 800, substrates 1404 and substrates 902 are the same (e.g.,substrate 1404-1 is implemented by substrate 902-1 and substrate 1404-2is implemented by substrate 902-2). In alternative examples, substrates1404 are different than substrates 902. Exemplary configurations ofmagnetic field generator 108 will be described below in more detail.Substrates 1404 are shown to have an octagonal shape. However,substrates 1404 may have any shape as may suit a particularimplementation.

A magnetic field sensing region 1406 is located in the gap (see FIG.14C). Magnetic field sensing region 1406 is a region where one or moremagnetometers 106 (including respective vapor cells 604) may be located.In some examples in which Bx′/By′ component generator 1400 is used incombination with Bz′ component generator 800, magnetic field sensingregion 1406 is the same as magnetic field sensing region 804.

A first wiring set 1408-1 is arranged on first substrate 1404-1 and asecond wiring set 1408-2 is arranged on second substrate 1404-2. Eachwiring set 1408 comprises a plurality of electrically unconnected wiresextending generally along the y-direction. Wiring sets 1408 may beformed of any suitable conductor of electrical current, such as metallicconductors (e.g., copper, silver, and/or gold) and non-metallicconductors (e.g., carbon). Wiring sets 1408 may be arranged onsubstrates 1404 in any suitable manner (e.g., etched, printed, soldered,deposited, or otherwise attached).

Interconnects 1410 (e.g., first interconnect 1410-1 and secondinterconnect 1410-2) are positioned between first substrate 1404-1 andsecond substrate 1404-2. Interconnects 1410 electrically connect firstwiring set 1408-1 with second wiring set 1408-2 to thereby form acontinuous electrical path (as represented by the dashed line in FIG.14C) through first wiring set 1408-1 and second wiring set 1408-2.Interconnects 1410 may electrically connect to wiring sets 1408 in byconnections 1414 (e.g., one or more relays, contact pads, wires, etc.).Interconnects 1410 may comprise any suitable electrical connectorconfigured to electrically connect first wiring set 1408-1 on firstsubstrate 1404-1 with second wiring set 1408-2 on second substrate1404-2. In some examples, each interconnect 1410 is an elastomericconnector that is anisotropically conductive in the z-direction.Suitable elastomeric connectors may include, for example, zebraconnectors commercially available from Fujipoly America Corp.

FIGS. 15A and 15B illustrate exemplary configurations of an elastomericconnector that may be used as interconnects 1410. As shown in FIG. 15A,a lamination-type elastomeric connector 1500A includes a plurality ofthin, planar conductive elements 1502, each of which is electricallyisolated from other conductive elements 1502 by intervening isolationelements 1504. Conductive elements 1502 may be formed of any suitableconductive material (e.g., silver, gold, copper, etc.). Isolationelements 1504 may be formed of any suitable electrically insulatingmaterial (e.g., an elastomeric material). Conductive elements 1502 andisolation elements 1504 are stacked in an alternating pattern. In someexamples, as shown in FIG. 15A, conductive elements 1502 and isolationelements 1504 are enclosed between side support barriers 1506-1 and1506-2. Side support barriers 1506 may also be formed of a suitableelectrically insulating material. When elastomeric connector 1500A ispositioned between substrates 1404, each conductive element 1502 isoriented in the z-direction and makes contact with first substrate1404-1 and second substrate 1404-2 (e.g., with contact pads on firstsubstrate 1404-1 and second substrate 1404-2).

FIG. 15B illustrates an exemplary matrix-type elastomeric connector1500B. Elastomeric connector 1500B is the same as elastomeric connector1500A except that conductive elements 1502 comprise fine conductivewires embedded within an elastomer matrix 1508.

Referring again to FIGS. 14A-14C, continuous electrical path 1412 formsa conductive winding configured to generate, when supplied with a drivecurrent, a Bx′ component of a compensation magnetic field. The Bx′component of the compensation magnetic field is configured to activelyshield magnetic field sensing region 1406 from ambient backgroundmagnetic fields along the x-axis. For example, Bx′/By′ componentgenerator 1400 may substantially reduce or cancel a Bx component ofambient background magnetic fields at magnetic field sensing region1406. In some examples, the Bx′ component of the compensation magneticfield is substantially equal and opposite to the Bx component of theambient background magnetic fields.

In alternative embodiments, Bx′/By′ component generator 1400 may beconfigured to generate a By′ component of the compensation magneticfield. FIGS. 16A-16C illustrate another exemplary configuration ofBx′/By′ component generator 1400. FIGS. 16A-16C are the same as FIGS.14A-14C except that wiring sets 1408 extend generally in thex-direction. Thus, continuous electrical path 1412 forms a conductivewinding configured to generate, when supplied with a drive current, aBy′ component of a compensation magnetic field. The By′ component of thecompensation magnetic field is configured to actively shield magneticfield sensing region 1406 from ambient background magnetic fields alongthe y-axis. For example, Bx′/By′ component generator 1400 maysubstantially reduce or cancel a By component of ambient backgroundmagnetic fields at magnetic field sensing region 1406. In some examples,the By′ component of the compensation magnetic field is substantiallyequal and opposite to the By component of the ambient backgroundmagnetic fields.

In some embodiments, Bx′/By′ component generator 1400 is configured toactively shield magnetic field sensing region 1406 from ambientbackground magnetic fields in both the x-direction and the y-direction.FIGS. 17A-17C show another exemplary configuration of Bx′/By′ componentgenerator 1400. FIGS. 17A-17C are the same as FIGS. 14A-14C except thata third wiring set 1408-3 is arranged on first substrate 1404-1 inaddition to first wiring set 1408-1, and a fourth wiring set 1408-4 isarranged on second substrate 1404-2 in addition to second wiring set1408-2. First wiring set 1408-1 and second wiring set 1408-2 extendgenerally in the y-direction while third wiring set 1408-3 and fourthwiring set 1408-4 extend generally in the x-direction. Interconnects1410-1 and 1410-2 electrically connect first wiring set 1408-1 withsecond wiring set 1408-2 to form a first continuous electrical path 1412through first wiring set 1408-1 and second wiring set 1408-2, andinterconnects 1410-3 and 1410-4 electrically connect third wiring set1408-3 with fourth wiring set 1408-4 to thereby form a second continuouselectrical path (not shown in FIG. 17C) through third wiring set 1408-3and fourth wiring set 1408-4. Interconnects 1410-3 and 1410-4 may beimplemented, for example, by an elastomeric connector, as describedabove. As shown in FIGS. 17A and 17B, interconnects 1410 are formed by asingle elastomeric connector that surrounds magnetic field sensingregion 1406. In other embodiments, interconnects 1410 are not connectedto one another but are separate structures.

As shown in FIG. 17C, first continuous electrical path 1412 forms afirst conductive winding configured to generate, when supplied with adrive current, a Bx′ component of a compensation magnetic field. Thesecond continuous electrical path (not shown) forms a second conductivewinding configured to generate, when supplied with a drive current, aBy′ component of the compensation magnetic field.

As shown in FIG. 17C, first wiring set 1408-1 and third wiring set1408-3 are both arranged on first substrate 1404-1, and second wiringset 1408-2 and fourth wiring set 1408-4 are both arranged on secondsubstrate 1404-2. In this embodiment, first wiring set 1408-1 isseparated from third wiring set 1408-3 by an electrical insulator (notshown) and second wiring set 1408-2 is separated from fourth wiring set1408-4 by an electrical insulator (not shown). In alternativeembodiments, first wiring set 1408-1 and third wiring set 1408-3 arearranged on opposite surface of first substrate 1404-1, and secondwiring set 1408-2 and fourth wiring set 1408-4 are arranged on oppositesurface of second substrate 1404-2. In yet other embodiments, eachwiring set 1408 is arranged on a different substrate.

In the examples described above, wiring sets 1408 (and hence conductivewindings formed by wiring sets 1408) may have any winding pattern as maysuit a particular implementation. In some examples the winding patternsof wiring sets 1408 may be automatically generated by a magnetic fieldgenerator design system configured to optimize the winding patternsbased on a set of inputs. An exemplary magnetic field generator designsystem will be described below in more detail. Generally, the windingpatterns of the Bx′ component and/or By′ component conductive windingsare configured to generate a homogeneous magnetic field at the magneticfield sensing region. The winding patterns may be configured to generatea homogeneous magnetic field that is approximately 30% the size ofwiring sets 1408, as measured along the x- or y-direction.

As mentioned above, in some embodiments magnetic field generator 108includes both Bz′ component generator 800 and Bx′/By′ componentgenerator 1400. With this configuration magnetic field generator 108 isconfigured to actively shield magnetic field sensing region 804/1406from ambient background magnetic fields along the x-, y-, and z-axes. Insome examples, conductive windings 802 of Bz′ component generator 800are arranged on substrates 1404 of Bx′/By′ component generator 1400. Insuch examples conductive windings 802 are electrically insulated fromwiring sets 1408. In alternative examples, conductive windings 802 ofBz′ component generator 800 are arranged on substrates (e.g., substrates902 of Bz′ component generator 800) that are different from substrates1404 of Bx′/By′ component generator 1400. An exemplary physicalimplementation of magnetic field generator 108 will be described belowin more detail.

As mentioned, magnetic field generator 108 is configured to activelyshield a magnetic sensing region from ambient magnetic fields along thex-, y, and/or z-axes. In some examples, magnetic field generator 108 isfurther configured to actively shield the magnetic sensing region fromfirst-order gradient magnetic fields, e.g., ambient background magneticfields that linearly vary in the x-, y-, and/or z-direction. The ambientbackground magnetic field B is a vector magnetic field that hasmagnitude and direction at each point in space. Using the Cartesiancoordinate system, ambient background magnetic field B can be expressedas:B=i·Bx+j·By+k·Bzwhere Bx, By and Bz are the Cartesian components of the ambientbackground magnetic field and i, j, and k are unit vectors along the x-,y-, and z-axes. The gradient of B, denoted VB, is a second order tensor,a matrix of nine partial derivatives of the three principal componentsof B (Bx, By, and Bz) with respect to the three cardinal axes (x, y, andz):

${\nabla B} = \begin{bmatrix}\frac{dBx}{dx} & \frac{dBy}{dx} & \frac{dBz}{dx} \\\frac{dBx}{dy} & \frac{dBy}{dy} & \frac{dBz}{dy} \\\frac{dBx}{dz} & \frac{dBy}{dz} & \frac{dBz}{dz}\end{bmatrix}$As can be seen from VB, there are nine possible gradient components ofthe ambient background magnetic fields. Accordingly, magnetic fieldgenerator 108 may further be configured to actively shield magneticfield sensing regions 804 and/or 1406 from any one or more of thegradient components of the ambient background magnetic fields. However,in some examples it is not necessary to generate every gradientcomponent of the compensation magnetic field. Instead, the gradientscomponents of the ambient background magnetic fields can be activelyshielded by generating a subset of gradient components of thecompensation magnetic field, as will now be described.

As mentioned above, Bz′ component generator 800 is configured togenerate one or more z-axis gradient components of the compensationmagnetic field when at least two conductive windings 802 (e.g.,conductive windings 802-1 and 802-2) are driven with different drivecurrents. For example, controller 104 may be configured to drive Bz′component generator 800 to generate a dBz′/dz gradient component, adBz′/dx gradient component, and/or a dBz′/dy gradient component of thecompensation magnetic field.

In some embodiments, Bx′/By′ component generator 1400 may also beconfigured to generate one or more gradient components of thecompensation magnetic field. FIGS. 18A-18C illustrate an exemplaryconfiguration of Bx′/By′ component generator 1400 having conductivewindings configured to generate gradient components of the compensationmagnetic field. FIGS. 18A and 18B show plan views (e.g., views in thez-direction) of Bx′/By′ component generator 1400, and FIG. 18C is aperspective view of various conductive windings included in Bx′/By′component generator 1400. Legend 1402 indicates an orientation of x-,y-, and z-axes. In FIGS. 18A-18C, wiring sets 1408 have been omitted tofacilitate discussion of the gradient component conductive windings.

As shown in FIG. 18A, first substrate 1404-1 includes a first gradientwiring 1802-1 extending generally in the y-direction along a first edgeof first substrate 1404-1 and a second gradient wiring 1802-2 extendinggenerally in the y-direction along a second edge of first substrate1404-1. First gradient wiring 1802-1 and second gradient wiring 1802-2are substantially parallel to each other and are represented by dashedlines. First substrate 1404-1 also includes a third gradient wiring1802-3 extending generally in the x-direction along a third edge offirst substrate 1404-1 and a fourth gradient wiring 1802-4 extendinggenerally in the x-direction along a fourth edge of first substrate1404-4. Third gradient wiring 1802-3 and fourth gradient wiring 1802-4are substantially parallel to each other and are represented bydash-dot-dash lines. Third gradient wiring 1802-3 and fourth gradientwiring 1802-4 are not electrically connected to first gradient wiring1802-1 or second gradient wiring 1802-1.

As shown in FIG. 18B, second substrate 1404-2 includes a fifth gradientwiring 1802-5 extending generally in the y-direction along a first edgeof second substrate 1404-2 and a sixth gradient wiring 1802-6 extendinggenerally in the y-direction along a second edge of second substrate1404-2. Fifth gradient wiring 1802-5 and sixth gradient wiring 1802-6are substantially parallel to each other and are represented by dashedlines. Second substrate 1404-2 also includes a seventh gradient wiring1802-7 extending generally in the x-direction along a third edge ofsecond substrate 1404-2 and an eighth gradient wiring 1802-8 extendinggenerally in the x-direction along a fourth edge of second substrate1404-2. Seventh gradient wiring 1802-7 and eighth gradient wiring 1802-8are substantially parallel to each other and are represented bydash-dot-dash lines. Seventh gradient wiring 1802-7 and eighth gradientwiring 1802-8 are not electrically connected to fifth gradient wiring1802-5 or sixth gradient wiring 1802-6.

Gradient wirings 1802 may each comprise one or more wires and may beformed of any suitable conductor of electrical current, such as metallicconductors (e.g., copper, silver, and/or gold) and non-metallicconductors (e.g., carbon). Gradient wirings 1802 may be arranged onsubstrates 1404 in any suitable manner (e.g., etched, printed, soldered,deposited, or otherwise attached). Furthermore, gradient wirings 1802may be arranged on any surfaces of substrates 1404 as may suit aparticular implementation.

When interconnects 1410 are positioned between first substrate 1404-1and second substrate 1404-2, as shown in FIGS. 17A-17C, interconnects1410 electrically connect gradient wirings 1802 on first substrate1404-1 with gradient wirings 1802 on second substrate 1404-2. Forexample, interconnects 1410 electrically connect first gradient wiring1802-1 with fifth gradient wiring 1802-5 to thereby form a firstcontinuous electrical path, which forms a first conductive winding1804-1, as shown in FIG. 18C. Similarly, interconnects 1410 electricallyconnect second gradient wiring 1802-2 with sixth gradient wiring 1802-6to thereby form a second continuous electrical path, which forms asecond conductive winding 1804-2. Interconnects 1410 also electricallyconnect third gradient wiring 1802-3 with seventh gradient wiring 1802-7to thereby form a third continuous electrical path, which forms a thirdconductive winding 1804-3. Interconnects 1410 further electricallyconnect fourth gradient wiring 1802-4 with eighth gradient wiring 1802-8to thereby form a fourth continuous electrical path, which forms afourth conductive winding 1804-4.

To generate a dBx′/dx gradient component of the compensation magneticfield, controller 104 drives first conductive winding 1804-1 and secondconductive winding 1804-2 with equal but opposite currents. Thecombination of the magnetic fields generated by conductive windings1804-1 and 1804-2 generates a dBx′/dx gradient component that linearlyvaries in the x-direction. Similarly, to generate a dBy′/dy gradientcomponent of the compensation magnetic field, controller 104 drivesthird conductive winding 1804-3 and fourth conductive winding 1804-4with equal but opposite currents. The combination of the magnetic fieldsgenerated by conductive windings 1804-3 and 1804-4 generates a dBy′/dygradient component that linearly varies in the y-direction.

Bx′/By′ component generator 1400 is further configured to generate acombination gradient component that is the sum of dBx′/dy and dBy′/dxgradient components of the compensation magnetic field. To this end,first substrate 1404-1 further includes a fifth conductive winding1804-5 that is formed of four L-shaped loops 1806 (e.g., loops 1806-1 to1806-4) positioned at each corner of first substrate 1404-1. In someexamples, as shown in FIGS. 18A-18C, loops 1806 are connected to eachother in series. Second substrate 1404-2 includes a sixth conductivewinding 1804-6 that is formed of four L-shaped loops 1806 (e.g., loops1806-5 to 1806-8) positioned at each corner of second substrate 1404-2.In some examples, as shown in FIGS. 18A-18C, loops 1806 are connected toeach other in series. Conductive windings 1804-5 and 1804-6 are notelectrically connected to each other, whether by interconnects 1410 orotherwise. Controller 104 may drive conductive windings 1804-5 and1804-6 with equal but opposite drive currents to thereby generate acombination gradient component that is the sum of dBx′/dy and dBy′/dxgradient components.

It will be recognized that the configuration of conductive windings 1804described above is merely exemplary and not limiting, as conductivewindings 1804 may have any other configuration or winding pattern as maysuit a particular implementation. Furthermore, in alternativeembodiments Bx′/By′ component generator 1400 may not include allconductive windings 1804. For example, if Bx′/By′ component generator1400 is configured to actively shield magnetic field sensing region 1406from ambient background magnetic fields in only the x-direction, Bx′/By′component generator 1400 may include only conductive windings 1804-1 and1804-2.

FIG. 19 shows an exemplary configuration 1900 in which wearable sensorunit 102 and controller 104 each include connection interfacesconfigured to facilitate wired connections therebetween. As shown,wearable sensor unit 102 includes a connection interface 1902 formagnetometers 106 and a connection interface 1904 for magnetic fieldgenerator 108. Controller 104 includes a connection interface 1906corresponding to connection interface 1902 and a connection interface1908 corresponding to connection interface 1904. Connection interfaces1902, 1904, 1906, and 1908 may each be implemented in any suitablemanner.

To illustrate, connection interface 1902 may be implemented by one ormore twisted pair cable interface assemblies electrically connected toone or more components within magnetometers 106, and connectioninterface 1906 may be implemented by one or more twisted pair cableinterface assemblies electrically connected to one or more componentswithin controller 104. In this configuration, communication links 110may be implemented by one or more twisted pair cables each including oneor more twisted pairs of wires that are configured to electricallyconnect specific components of magnetometers 106 and/or other elementsof wearable sensor unit 102 with specific components of controller 104.The one or more twisted pair cable interface assemblies of wearablesensor unit 102 and controller 104 may each be configured to connect toa twisted pair cable in any suitable manner.

In this configuration, controller 104 may be configured to interfacewith one or more components included in magnetometers 106 and/or otherelements of wearable sensor unit 102 by transmitting signals to the oneor more components over one or more twisted pair cables and/or receivingsignals from the one or more components over the one or more twistedpair cables.

To illustrate, FIG. 20 shows an exemplary configuration 2000 in whichcontroller 104 interfaces with various components of or associated witha particular magnetometer 106 by way of a plurality of twisted paircable interfaces 2002 (e.g., twisted pair cable interfaces 2002-1through 2002-4) included in wearable sensor unit 102. As shown, twistedpair cable interface 2002-1 is electrically connected to an input oflight source 602 (described above in connection with FIG. 6), twistedpair cable interface 2002-2 is electrically connected to an input of aheater 2004 for light source 602, twisted pair cable interface 2002-3 iselectrically connected to an output of a thermistor 2006 for lightsource 602, and twisted pair cable interface 2002-4 is electricallyconnected to an output of a monitor photodetector 2008 for light source602.

As mentioned, light source 602 is configured to generate and outputlight that enters and exits (e.g., by passing through) vapor cell 604(not shown in FIG. 20). To control (e.g., drive) light source 602,controller 104 may supply a drive current to the input of light source602 by way of twisted pair cable interface 2002-1. For example, thisdrive current may be supplied by controller 104 over a twisted pair ofwires included in a twisted pair cable connected to twisted pair cableinterface 2002-1.

As shown, the light output by light source 602 may be detected bymonitor photodetector 2008, which is configured to detect the lightbefore the light enters vapor cell 604 and output current representativeof the detected light. Controller 104 may use the output of monitorphotodetector 2008 to monitor and compensate for a behavior of lightsource 602 in any suitable manner. For example, based on the output ofmonitor photodetector 2008, controller 104 may adjust the drive currentprovided to light source 602.

Controller 104 may be configured to read an output of monitorphotodetector 2008 by way of twisted pair cable interface 2002-4. Forexample, controller 104 may receive the current output by monitorphotodetector 2008 over a twisted pair of wires included in a twistedpair cable connected to twisted pair cable interface 2002-4.

Heater 2004 may be configured to apply heat to light source 602. To thisend, heater 2004 may be thermally coupled to light source 602. Tocontrol (e.g., drive) heater 2004, controller 104 may supply a drivecurrent to the input of heater 2004 by way of twisted pair cableinterface 2002-2. For example, this drive current may be supplied bycontroller 104 over a twisted pair of wires included in a twisted paircable connected to twisted pair cable interface 2002-2.

Thermistor 2006 may be configured to detect the operating temperature oflight source 602 and output current representative of the operatingtemperature. To this end, thermistor 2006 may be thermally coupled tolight source 602. Controller 104 may be configured to read an output ofthermistor 2006 by way of twisted pair cable interface 2002-3. Forexample, controller 104 may receive the current output by thermistor2006 over a twisted pair of wires included in a twisted pair cableconnected to twisted pair cable interface 2002-3.

Heater 2004 and thermistor 2006 may be used by controller 104 to controlan operating temperature of light source 602. For example, heater 2004and thermistor 2006 may be used to temperature control light source 602down to a particular threshold (e.g., within one millikelvin oftemperature stability).

Any of the twisted pair cable interfaces 2002 shown in FIG. 20 may beused by controller 104 to interface with multiple components withinwearable sensor unit 102. For example, twisted pair cable interface2002-1 may be used to supply drive current to all of the light sources602 included in an array of magnetometers 106. To illustrate, if thereare twenty-five light sources 602 included in wearable sensor unit 102,twisted pair cable interface 2002-1 may include twenty-five pairs oftwisted wire each configured to be used by controller 104 to supplydrive current to a different one of the twenty-five light sources 602.Likewise, twisted pair cable interface 2002-2 may be used to interfacewith a plurality of heaters 2004, twisted pair cable interface 2002-3may be used to interface with a plurality of thermistors 2006, andtwisted pair cable interface 2002-4 may be used to interface with aplurality of monitor photodiodes 2008.

FIG. 21 shows another exemplary configuration 2100 in which controller104 interfaces with various components of a particular magnetometer 106by way of a plurality of twisted pair cable interfaces 2002 included inwearable sensor unit 102. FIG. 21 is similar to FIG. 6 in that itdepicts light source 602, vapor cell 604, signal photodetector 606, andheater 608. However, FIG. 21 further shows that a twisted pair cableinterface 2002-5 is electrically connected to an input of heater 608 anda twisted pair cable interface 2002-6 is electrically connected to anoutput of signal photodetector 606.

In configuration 2100, controller 104 may control (e.g., drive) heater608 by supplying a drive current to the input of heater 608 by way oftwisted pair cable interface 2002-5. For example, this drive current maybe supplied by controller 104 over a twisted pair of wires included in atwisted pair cable connected to twisted pair cable interface 2002-5.Controller 104 may read an output of signal photodetector 606 by way oftwisted pair cable interface 2002-6. For example, controller 104 mayreceive the current output by signal photodetector 606 over a twistedpair of wires included in a twisted pair cable connected to twisted paircable interface 2002-6. As described above, twisted pair cableinterfaces 2002-5 and 2002-6 may in some examples be used to interfacewith multiple heaters 608 and signal photodetectors 606, respectively.

Returning to FIG. 19, in some examples, connection interface 1904 andconnection interface 1908 are each implemented by one or more coaxialcable interface assemblies. In this configuration, communication link112 may be implemented by one or more coaxial cables each configured toelectrically connect specific components of magnetic field generator 108with specific components of controller 104. The one or more coaxialcable interface assemblies of wearable sensor unit 102 and controller104 may each be configured to connect to a coaxial cable in any suitablemanner.

To illustrate, FIG. 22 shows an exemplary configuration 2200 in whichcontroller 104 interfaces with various components of magnetic fieldgenerator 108 by way of a plurality of coaxial cable interfaces 2202(e.g., coaxial cable interfaces 2202-1 and 2202-2) included in wearablesensor unit 102. As shown, a coaxial cable 2204-1 is connected tocoaxial cable interface 2202-1 and to controller 104 (e.g., a coaxialcable interface that implements connection interface 1908). Likewise, acoaxial cable 2204-2 is connected to coaxial cable interface 2202-2 andto controller 104 (e.g., another coaxial cable interface that implementsconnection interface 1908).

In this configuration, controller 104 may supply a drive current to afirst conductive winding 2206-1 included in magnetic field generator 108by way of conductive path 2208-1. Likewise, controller 104 may supply adrive current to a second conductive winding 2206-2 included in magneticfield generator 108 by way of conductive path 2208-2. Conductive paths2208-1 and 2208-2 may be implemented, for example, by center pinsincluded in coaxial cables 2204-1 and 2204-2, respectively. In someexamples, as shown in FIG. 22, conductive return paths 2210-1 and 2210-2(which may be implemented by conductive braids included in coaxialcables 2204) may be connected such that the return paths are common forboth conductive windings 2206. In this manner, the potential of all ofthe return paths is maintained at ground, which may be advantageous forsuppression of fringe magnetic fields. Moreover, this configuration mayprevent conductive windings 2206 from having to be insulated from eachother to maintain a nonzero potential with respect to each other.However, in some alternative embodiments, the return paths forconductive windings 2206 are not conductively connected.

In the configuration shown in FIG. 22, conductive windings 2206 areconfigured to generate one of the components (e.g., the Bz′ component)of the compensation magnetic field used to actively shield magnetometers106 from ambient background magnetic fields. Such conductive windingsmay be implemented by two half-coils and/or in any other suitablemanner. Other conductive winding configurations may be driven overcoaxial cables in any suitable manner.

Use of twisted pair cables to interface with magnetometers 106 andcoaxial cables to interface with magnetic field generator 108 isbeneficial for a number of reasons. For example, intended operation of amagnetometer, such as an OPM, may include a modulated drive currentapplied to conductive windings, resulting in a modulated magnetic field,resulting in a modulated optical transmission by alkali metal atoms,resulting in modulated light intensity at the signal photodetector,resulting in modulated output of the photodetector measurementcircuitry. Any alternate path for the modulation signal to couple intothe photodetector measurement may degrade the quality of themagnetometer measurement. Hence, by using coaxial cables to drivemagnetic field generator 108 and twisted pair cables to read the outputof the signal photodetectors 606, the coupling potential of therelatively long parallel cables that carry the conductive winding drivecurrents and the signal photodetector signals may be minimized oreliminated.

Moreover, by using coaxial cables to drive magnetic field generator 108with the coaxial cable shields held at a constant electric potential,the electric field external to the coaxial cables is not affected by themodulation signal inside the coaxial cables. The result is that thetwisted pair cable used to read the output of the signal photodetectors606 will not be affected by the modulation signal.

Furthermore, by using coaxial cables to drive magnetic field generator108, no magnetic fields are generated by signals carried by the coaxialcables that would interfere with the operation of magnetometers 106. Thetwisted pair cables that interface with the magnetometers 106 maygenerate magnetic fields, but because the signals on the twisted paircables are alternating current (AC), the resultant magnetic fieldsgenerated by the twisted pair cables are at a relatively high frequencythat is out of the sensitivity range of magnetometers 106. Moreover,although coaxial cables are susceptible to environmental noise, suchenvironmental noise is rejected by twisted pair cables. Hence, crosstalkbetween the coaxial and twisted pair cables may be minimized orprevented.

Referring again to FIG. 19, connection interface 1904 and connectioninterface 1908 may alternatively be implemented by one or more twistedpair interface assemblies. In these alternative configurations,communication link 112 may be implemented by one or more twisted paircables each configured to electrically connect specific components ofmagnetic field generator 108 with specific components of controller 104.In these alternative configurations, magnetic field generator 108 may bedriven by controller 104 in a balanced manner so that the common modevoltage on the twisted pair cables are minimized. Moreover, in thisconfiguration, electrical coupling from the twisted pairs of wires thatare used to drive magnetic field generator 108 to the twisted pairs ofwires that are used to read signal photodetectors 608 may not result inthe modulation signal being measured on the signal photodetectors 608.However, for illustrative purposes, it will be assumed in the examplesprovided herein that connection interface 1904 and connection interface1908 are each implemented by one or more coaxial cable interfaceassemblies.

Exemplary manners in which controller 104 may measure current output byone or more photodetectors included in wearable sensor unit 102 will nowbe described. FIG. 23 illustrates an exemplary configuration 2300 inwhich controller 104 includes a plurality of differential signalmeasurement circuits 2302 (e.g., differential signal measurementcircuits 2302-1 through 2302-N) configured to measure current output byphotodetectors 2304 (e.g., photodetectors 2304-1 through 2304-N)included in magnetometers 106 (e.g., magnetometers 106-1 through 106-N).Differential signal measurement circuits 2302 may be included, forexample, on one or more PCBs included in a housing of controller 104.

In configuration 2300, photodetectors 2304 may each be implemented by asignal photodetector (e.g., signal photodetector 606) or by a monitorphotodetector (e.g., monitor photodetectors 2008). As described herein,a signal photodetector is configured to detect light output by a lightsource (e.g., light source 602) in a magnetometer after the light entersand exits (e.g., by passing through) a vapor cell (e.g., vapor cell 604)of the magnetometer. A monitor photodetector is configured to detect thelight output by the light source before the light enters the vapor cell.

In configurations where magnetometers 106 each include a signalphotodetector and a monitor photodetector, controller 104 may include adifferent differential signal measurement circuit 2302 for each of thephotodetectors. For example, if wearable sensor unit 102 includes anarray of twenty-five magnetometers 106 each having a signalphotodetector and a monitor photodetector, controller 104 may includetwenty-five differential signal measurement circuits 2302 for thetwenty-five signal photodetectors and twenty-five differential signalmeasurement circuits 2302 for the twenty-five monitor photodetectors.

As shown in FIG. 23, differential signal measurement circuits 2302 mayeach be electrically connected to the output of its correspondingphotodetector 2304 by way of a communication link 2306. For example,differential signal measurement circuit 2302-1 is electrically connectedto the output of photodetector 2304-1 by way of communication link2306-1, differential signal measurement circuit 2302-1 is electricallyconnected to the output of photodetector 2304-2 by way of communicationlink 2306-2, and differential signal measurement circuit 2302-N iselectrically connected to the output of photodetector 2304-N by way ofcommunication link 2306-N. In some examples, communication links 2306are each implemented by twisted pairs of wires. The twisted pairs ofwires may be included in one or more twisted pair cables, as describedherein.

Differential signal measurement circuits 2302 may each be implemented inany suitable manner. For example, differential signal measurementcircuits 2302 may each be implemented by a differential transimpedanceamplifier (TIA) circuit.

To illustrate, FIG. 24 shows an exemplary configuration 2400 in whichcontroller 104 includes circuitry configured to measure current outputby photodetector 2304-1. As shown, the circuitry includes a TIA circuit2402, a DC decoupling filter 2404, and an analog-to-digital (ADC) driver2406.

TIA circuit 2402 is connected to photodetector 2304-1 by way of atwisted pair of wires 2408-1 and 2408-2. TIA circuit 2402 is configuredto measure a difference between current coming in to TIA circuit 2402 onwire 2408-1 and current going out from TIA circuit 2402 on wire 2408-2.TIA circuit 2402 may be implemented by any suitable combination ofelectronic components and is merely illustrative of the many differentmanners in which differential signal measurement circuits 2302 may beimplemented.

DC decoupling filter 2404 may be implemented in any suitable manner andmay be configured to perform one or more DC decoupling filteringoperations as may serve a particular implementation. ADC driver 2406 maybe implemented in any suitable manner and may be configured to outputvoltages Voutp and Voutn, which may be used to drive an ADC that outputsa digital representation of the current measured by TIA circuit 2402.

By measuring a difference between current coming in to TIA circuit 2402on wire 2408-1 and current going out from TIA circuit 2402 on wire2408-2, TIA circuit 2402 (or, alternatively, any other implementation ofdifferential signal measurement circuits 2302) may minimize or eliminatean effect of environmental noise (e.g., noise currents induced byexternal electrical fields) that may couple onto the twisted pair ofwires 2408. This is because such noise couples equally into both sidesof TIA circuit 2402 due to matched input impedances of the TIA circuit2402. Hence, when the difference between the currents on wires 2408-1and 2408-2 is measured, the noise shows up as a common mode signal andis rejected.

Because of this, a cable (e.g., a twisted pair cable) used to connectphotodetectors 2304 to differential signal measurement circuits 2302does not need to be shielded to prevent environmental noise from beingcoupled into the cable. By not having to shield the cable, the cable maybe less thick and/or more flexible compared to a shielded cable, whichis beneficial to a user of the wearable sensor unit 102. Hence, in someconfigurations, one or more cables (e.g., twisted pair cables) used toelectrically connect controller 104 to wearable sensor unit 102 areunshielded.

In some examples, interfacing by controller 104 with various componentsof wearable sensor unit 102 is performed using AC instead of directcurrent (DC). This may prevent magnetic fields generated by DC frominterfering with an operation of magnetometers 106. Although AC alsogenerates magnetic fields, these magnetic fields are at a relativelyhigh frequency (e.g., 200 kHz) and therefore do not affect the operationof magnetometers 106, which, in some examples, are only sensitive up toa couple hundred Hertz.

For example, controller 104 may be configured to supply AC drive currentto light source 602, heater 2004, and/or heater 608. To illustrate, FIG.25 shows exemplary circuitry that may be included in controller 104 andused to supply a drive current to a heater (e.g., heater 2004 or heater608) included in wearable sensor unit 102. As shown, a DC DAC 2502creates a DC control voltage proportional to the amount of heat that isto be produced by the heater. A square wave generator 2504 (e.g., aswitch) chops the control voltage at a frequency F1 (which may be anysuitable frequency) to create an AC voltage. A bandpass filter 2506removes higher order harmonics from the AC voltage. An amplifier circuit2508-1 uses the AC voltage to drive a first wire 2510-1 of a twistedpair of wires that interconnects controller 104 and a chip resistor 2512included in wearable sensor unit 102 and connected to the heater. Aninverting amplifier 2508-2 uses the AC voltage to drive a second wire2510-2 of the twisted pair of wires. In this manner, the chip resistor2512 and the heater may be driven with a desired amount of AC.

Controller 104 may also be configured to use AC to detect current outputby various components of wearable sensor unit 102. For example,controller 104 may use AC to detect current output by thermistor 2006,monitor photodetector 2008, and/or signal photodetector 606. Toillustrate, to read the output of thermistor 2006, controller 104 may beconfigured to drive an AC voltage through a Wheatstone Bridge (or anyother suitable circuitry) and measure a resulting voltage acrossthermistor 2006.

Additionally, to minimize magnetic field spread, the physical areaenclosed by an outgoing current line and a return current line on aprinted circuit board (e.g., a printed circuit board that includes lightsources and/or photodetectors) may be designed to be less than athreshold amount (e.g., the distance between the two current lines maybe less than 2 mm).

FIG. 26 shows a perspective view of an exemplary physical implementation2600 of wearable sensor unit 102. As shown, physical implementation 2600includes PCBs 2602-1 and 2602-2 (collectively “PCBs 2602”) andsubstrates 2604-1 through 2604-4 (collectively “substrates 2604”). Insome examples, substrates 2604 may be implemented by PCBs.

PCBs 2602 and substrates 2604 are structurally arranged as shown. Inparticular, PCB 2602 is located at a “top” side of physicalimplementation 2600 (i.e., a side furthest away from a head or othersurface upon which wearable sensor unit 102 is placed to detect magneticfields) and substrate 2604-2 is located at a “bottom” side of physicalimplementation 2600 (i.e., a side closest to a head or other surfaceupon which wearable sensor unit 102 is placed to detect magneticfields).

Interconnect 2605 is disposed between substrates 2604-3 and 2604-5 andmaintains a spacing between substrates 2604-3 and 2604-5. A magneticfield sensing region (not shown in FIG. 26) is located betweensubstrates 2604-3 and 2604-5 and surrounded by interconnect 2605. Anarray of vapor cells (not shown) is located within the magnetic fieldsensing region.

Conductive windings that constitute magnetic field generator 108 aredisposed on substrates 2604. For example, conductive windings configuredto generate the Bz′ component of the compensation magnetic field may bedisposed on substrates 2604-1 and 2604-2. Conductive windings configuredto generate the Bx′ and By′ components of the compensation magneticfield include wiring sets disposed on substrates 2604-3 and 2604-4 andconductive elements in interconnect 2605. Conductive windings configuredto generate gradient components of the compensation magnetic field mayadditionally be disposed on substrates 2604-1 through 2604-4 and ininterconnect 2605.

PCB 2602-1 includes various components disposed thereon that areassociated with light sources included in each magnetometer 106. Forexample, PCB 2602-1 may include light sources (e.g., light source 602),heaters (e.g., heater 2004) for the light sources, thermistors (e.g.,thermistor 2006) for the light sources, and monitor photodetectors(e.g., monitor photodetector 2008) disposed thereon. As shown, PCB2602-1 may also include a plurality of twisted pair cable interfaceassemblies 2606 disposed thereon. In particular, twisted pair cableinterface assembly 2606-1 is electrically connected to inputs of thelight sources, twisted pair cable interface 2606-2 is electricallyconnected to inputs of the heaters, twisted pair cable interface 2606-3is electrically connected to outputs of the thermistors, and twistedpair cable interface 2606-4 is electrically connected to outputs of themonitor photodetectors.

PCB 2602-2 may include signal photodetectors (e.g., signal photodetector606) and a twisted pair cable interface 2606-5 electrically connected tooutputs of the signal photodetectors. A twisted pair cable interface2606-6 electrically connected to inputs of heaters (e.g., heater 608)for the signal photodetectors is disposed on a mount 2608 locatedproximate to PCB 2602-2.

As shown, coaxial cable interface assemblies 2610-1 through 2610-9(collectively “coaxial cable interface assemblies 2610”) are located onsubstrates 2604. Coaxial cable interface assemblies 2610 areconductively coupled to the conductive windings that constitute magneticfield generator 108. As described herein, controller 104 may drive theconductive windings by supplying drive current to the conductivewindings by way of coaxial cables connected to coaxial cable interfaceassemblies 2610.

Physical implementation 2600 may include any additional or alternativecomponents as may suit a particular implementation (e.g., a housing tohouse at least some of the components shown in FIG. 26, supportstructures to support substrates 2604, etc.).

FIG. 27 shows a cross sectional side view of physical implementation2600 of wearable sensor unit 102 and illustrates various components ofmagnetometers 106 that are located within wearable sensor unit 102.

For example, FIG. 27 shows that a plurality of light sources (e.g.,light source 2702, which may implement any of the light sourcesdescribed herein), a plurality of thermistors (e.g., thermistor 2704,which may implement any of the thermistors described herein), and aplurality of monitor photodetectors (e.g., monitor photodetector 2706,which may implement any of the monitor photodetectors described herein)are disposed on an underneath side of PCB 2602-1.

Light generated by light sources is collimated by a plurality ofcollimating lenses (e.g., collimating lens 2708) and passes throughoptics (e.g., optics 2710). Optics may include, for example, a prism foreach magnetometer that is configured to reflect the light onto themonitor photodiodes. The light also passes through the optics, thenthrough holes (e.g., hole 2712) in substrate 2604-3, then throughchimneys (e.g., chimney 2714), and into vapor cells (e.g., vapor cell2716, which may implement any of the vapor cells described herein). Thechimneys are configured to prevent heat from the vapor cells from goingback up through the holes.

In the implementation of FIG. 27, the light from the light sourcespasses through the vapor cells, then through a second set of chimneys(e.g., chimney 2718), and then through holes (e.g., hole 2720) insubstrate 2604-4. The light is then detected by signal photodetectors(e.g., signal photodetector 2722, which may implement any of the signalphotodetectors described herein).

FIG. 28 shows an exemplary configuration 2800 in which wearable sensorunit 102 further includes a temperature control circuit 2802.Temperature control circuit 2802 is configured to create a temperaturegradient within each of the vapor cells of magnetometers 106. Thetemperature gradient is configured to concentrate the alkali metalwithin each of the vapor cells away from transit paths of light thatpasses into the vapor cells. As described herein, this may allow thelight to properly enter and exit the vapor cells and then be detected bysignal photodetectors. In some examples, controller 104 is configured todrive temperature control circuit 2802 by supplying current totemperature control circuit 2802.

Temperature control circuit 2802 may be configured to create atemperature gradient within a vapor cell in any suitable manner. Forexample, temperature control circuit 2802 may be configured to createthe temperature gradient within the vapor cell by creating anycombination of hot spots, cold spots, distributed cooling, and/ordistributed heating.

To illustrate, in some examples, temperature control circuit 2802 may beconfigured to create a temperature gradient within a vapor cell bycreating one or more hot spots on an inner surface of the vapor cellthat are hotter by at least a threshold amount (e.g., a threshold numberof degrees) than other locations on the inner surface of the vapor cell.In these examples, temperature control circuit 2802 may, in someembodiments, also apply distributed cooling to at least some of theother locations on the inner surface of the vapor cell and/or create oneor more cold spots on the inner surface of the vapor cell that arecolder by at least a threshold amount than other locations on the innersurface of the vapor cell.

In some alternative examples, temperature control circuit 2802 may beconfigured to create a temperature gradient within a vapor cell bycreating one or more cold spots on an inner surface of the vapor cellthat are colder by at least a threshold amount than other locations onthe inner surface of the vapor cell. In these examples, temperaturecontrol circuit 2802 may, in some embodiments, also apply distributedheating to at least some of the other locations on the inner surface ofthe vapor cell and/or create one or more hot spots on the inner surfaceof the vapor cell that are hotter by at least an additional thresholdamount than other locations on the inner surface of the vapor cell.

To illustrate the benefits of creating a temperature gradient within avapor cell, FIG. 29 shows an exemplary configuration 2900 in which avapor cell 2902 (which may implement any of the vapor cells describedherein) includes an input window 2904 on a top surface 2906 of vaporcell 2902 and an output window 2908 on a bottom surface 2910 of vaporcell 2902. Input window 2904 and output window 2908 may be made out ofany suitable material that allows light to pass therethrough.

As shown, a light source 2912 (which may implement any of the lightsources described herein) outputs light 2914 (e.g., a light beam)configured to enter vapor cell 2904 through input window 2904 along atransit path 2916. The light 2914 is intended to continue along transitpath 2916 until it exits vapor cell 2902 through output window 2908. Thelight 2914 is then detected by a signal photodetector 2918, which mayimplement any of the signal photodetectors described herein.

As described herein, vapor cell 2902 contains alkali metal, which isrepresented in FIG. 29 by a plurality of X's interspersed within vaporcell 2902. The alkali metal may have any combination of gas, liquid, andsolid states, depending on temperature. In some instances duringoperation of the magnetometer of which vapor cell 2902 is a part, ifatoms of the alkali metal are within transit path 2916, the alkali metalmay potentially prevent light 2914 from properly exiting vapor cell 2902through output window 2908.

FIG. 30 shows an exemplary configuration 3000 in which temperaturecontrol circuit 2802 creates a temperature gradient within vapor cell2902 that concentrates the alkali metal within vapor cell 2902 away fromtransit path 2916 of light 2914. In configuration 3000, temperaturecontrol circuit 2802 is implemented by a PCB 3002 that includes an inputaperture 3004-1 configured to align with and be above input window 2904of vapor cell 2902 such that light 2914 passes through input aperture3004-1 before passing through input window 2904, a heat generatingelement 3006-1 configured to generate heat, a thermal contact 3008-1 ona first side of input aperture 3004-1 and thermally connected to heatgenerating element 3006-1, and a thermal path out 3010-1 on a secondside of input aperture 3004-1. Heat generating element 3006-1, thermalcontact 3008-1, and thermal path out 3010-1 have dashed lines in FIG. 30to connote that they may be disposed on an underneath side of PCB 3002.

Heat generating element 3006-1 may be implemented by one or moreelectrical components configured to generated heat when driven with acurrent by controller 104. For example, heat generating element 3006-1may be implemented by one or more resistors.

Thermal contact 3008-1 is configured to create one or more hot spots bydirecting the heat from heat generating element 3006-1 to vapor cell2902. Thermal path out 3010-1 provides a path for heat to escape and isconfigured to assist in creating the temperature gradient within vaporcell 2902. In some examples, PCB 3002 is positioned close enough to topsurface 2906 of vapor cell 2902 that thermal contact 3008-1 and thermalpath out 3010-1 are in physical contact with top surface 2906.

In configuration 3000, the temperature gradient created by one or morehot spots is configured to concentrate the alkali metal within vaporcell 2902 at the relatively colder regions within vapor cell 2902, whichare closer to thermal path out 3010-1 than to thermal contact 3008-1.This is illustrated in FIG. 30 by the Xs that represent the alkali metalbeing concentrated on the right side of vapor cell 2902, away fromtransit path 2916.

FIG. 31 illustrates another implementation 3100 of temperature controlcircuit 2802. In implementation 3100, PCB 3002 is flexible andconfigured to fold along bend lines 3102-1 and 3102-2 to surround vaporcell 2902. In this configuration, PCB 3002 further includes an outputaperture 3004-2 configured to align with and be below output window 2908of vapor cell 2902 such that light 2914 passes through output aperture3004-2 after passing through output window 2908, a heat generatingelement 3006-2 configured to generate heat, a thermal contact 3008-2 ona first side of output aperture 3004-2 and thermally connected to heatgenerating element 3006-2, and a thermal path out 3010-2 on a secondside of output aperture 3004-2.

Heat generating element 3006-2 may be implemented by one or moreelectrical components configured to generated heat when driven with acurrent by controller 104. For example, heat generating element 3006-2may be implemented by one or more resistors. Because heat generatingelements 3006-1 and 3006-2 are on the same PCB 3002, they may be drivenconcurrently by controller 104 with the same current.

Thermal contact 3008-2 is configured to assist in creating the one ormore hot spots by directing the heat from heat generating element 3006-2to vapor cell 2902. Thermal path out 3010-2 provides a path for heat toescape and is configured to assist in creating the temperature gradientwithin vapor cell 2902. In some examples, PCB 3002 is positioned closeenough to bottom surface 2910 of vapor cell 2902 that thermal contact3008-2 and thermal path out 3010-2 are in physical contact with bottomsurface 2910.

FIG. 32 is a perspective view of an exemplary flexible PCBimplementation 3200 of temperature control circuit 2802 that may be usedin a wearable sensor unit that includes an array of twenty-fivemagnetometers. As shown, implementation 3200 includes a flexible PCB3202 configured to fold along fold lines 3204-1 and 3204-2 such that atop portion 3206-1 of flexible PCB 3202 is configured to be positionedabove an array of vapor cells (e.g., an array of vapor cells similar tovapor cell 2902) and a bottom portion 3206-2 of flexible PCB 3202 isconfigured to be positioned below the array of vapor cells.

As shown, top portion 3206-1 of flexible PCB 3202 includes a pluralityof input apertures (e.g., input aperture 3208-1), a plurality of heatgenerating elements (e.g., heat generating elements 3210-1 and 3210-2),a plurality of thermal contacts (e.g., thermal contacts 3212-1 and3212-2), and a plurality of thermal paths out (e.g., thermal path out3214-1). Likewise, bottom portion 3206-2 of flexible PCB 3202 includes aplurality of output apertures (e.g., output aperture 3208-2), aplurality of heat generating elements (e.g., heat generating elements3210-3 and 3210-4), a plurality of thermal contacts (e.g., thermalcontacts 3212-3 and 3212-4), and a plurality of thermal paths out (e.g.,thermal path out 3214-2).

While flexible PCB 3202 is in the folded position, elements on topportion 3206-1 of flexible PCB 3202 corresponding to elements on bottomportion 3206-2 of flexible PCB 3202 may align with each other and withindividual vapor cells included the array of vapor cells. For example,while flexible PCB 3202 is in the folded position, input aperture 3208-1and output aperture 3208-2 are configured to be aligned with input andoutput windows of a particular vapor cell.

While flexible PCBs used to implement temperature control circuit 2802are shown in FIGS. 31 and 32, in alternative implementations, separatePCBs with heating and/or cooling elements may be located above andbeneath the vapor cells of wearable sensor unit 102.

FIG. 33 illustrates an alternative configuration 3300 in which a vaporcell 3302 does not include an output window on a bottom surface of thevapor cell 3302. Instead, as shown, vapor cell 3302 includes a singlewindow 3304 on a top surface 3306. A reflecting element 3308 (e.g., amirror) is located on a bottom surface 3310 of vapor cell 3302 (i.e., atan opposite end of vapor cell 3302 than window 3304).

In configuration 3300, light 3312 output by a light source 3314 entersvapor cell 3302 through window 3304, reflects off of reflecting element3308, and exits vapor cell 3302 through the same window 3304. A signalphotodetector 3318 may then detect reflected light 3316. The temperaturecontrol circuit 2802 described herein may be used to concentrate alkalimetal within vapor cell 3302 away from a transit path 3316 of light 3312in any of the ways described herein.

FIGS. 34-39 illustrate embodiments of a wearable device 3400 thatincludes elements of the wearable sensor units described herein. Inparticular, the wearable devices 3400 include a plurality ofmagnetometers 3402 and a magnetic field generator (not shown). Thewearable devices 3400 may each also include a controller (e.g.,controller 104) and/or be communicatively connected to a controller. Ingeneral, wearable device 3400 may be implemented by any suitableheadgear and/or clothing article configured to be worn by a user. Theheadgear and/or clothing article may include batteries, cables, and/orother peripherals for the components of the wearable sensor unitsdescribed herein.

FIG. 34 illustrates an embodiment of a wearable device 3400 in the formof a helmet with a handle 3404. A cable 3406 extends from the wearabledevice 3400 for attachment to a battery or hub (with components such asa processor or the like). FIG. 35 illustrates another embodiment of awearable device 3400 in the form of a helmet showing a back view. FIG.36 illustrates a third embodiment of a wearable device 3400 in the formof a helmet with the cable 3406 leading to a wearable garment 3408 (suchas a vest or partial vest) that can include a battery or a hub.Alternatively or additionally, the wearable device 3400 can include acrest 3410 or other protrusion for placement of the hub or battery.

FIG. 37 illustrates another embodiment of a wearable device 3400 in theform of a cap with a wearable garment 3408 in the form of a scarf thatmay contain or conceal a cable, battery, and/or hub. FIG. 38 illustratesadditional embodiments of a wearable device 3400 in the form of a helmetwith a one-piece scarf 3408 or two-piece scarf 3408-1. FIG. 39illustrates an embodiment of a wearable device 3400 that includes a hood3410 and a beanie 3412 which contains the magnetometers 3402, as well asa wearable garment 3408 that may contain a battery or hub.

In some examples, a non-transitory computer-readable medium storingcomputer-readable instructions may be provided in accordance with theprinciples described herein. The instructions, when executed by aprocessor of a computing device, may direct the processor and/orcomputing device to perform one or more operations, including one ormore of the operations described herein. Such instructions may be storedand/or transmitted using any of a variety of known computer-readablemedia.

A non-transitory computer-readable medium as referred to herein mayinclude any non-transitory storage medium that participates in providingdata (e.g., instructions) that may be read and/or executed by acomputing device (e.g., by a processor of a computing device). Forexample, a non-transitory computer-readable medium may include, but isnot limited to, any combination of non-volatile storage media and/orvolatile storage media. Exemplary non-volatile storage media include,but are not limited to, read-only memory, flash memory, a solid-statedrive, a magnetic storage device (e.g. a hard disk, a floppy disk,magnetic tape, etc.), ferroelectric random-access memory (“RAM”), and anoptical disc (e.g., a compact disc, a digital video disc, a Blu-raydisc, etc.). Exemplary volatile storage media include, but are notlimited to, RAM (e.g., dynamic RAM).

FIG. 40 illustrates an exemplary computing device 4000 that may bespecifically configured to perform one or more of the processesdescribed herein. Any of the systems, units, computing devices, and/orother components described herein may be implemented by computing device4000.

As shown in FIG. 40, computing device 4000 may include a communicationinterface 4002, a processor 4004, a storage device 4006, and aninput/output (“I/O”) module 4008 communicatively connected one toanother via a communication infrastructure 4010. While an exemplarycomputing device 4000 is shown in FIG. 40, the components illustrated inFIG. 40 are not intended to be limiting. Additional or alternativecomponents may be used in other embodiments. Components of computingdevice 4000 shown in FIG. 40 will now be described in additional detail.

Communication interface 4002 may be configured to communicate with oneor more computing devices. Examples of communication interface 4002include, without limitation, a wired network interface (such as anetwork interface card), a wireless network interface (such as awireless network interface card), a modem, an audio/video connection,and any other suitable interface.

Processor 4004 generally represents any type or form of processing unitcapable of processing data and/or interpreting, executing, and/ordirecting execution of one or more of the instructions, processes,and/or operations described herein. Processor 4004 may performoperations by executing computer-executable instructions 4012 (e.g., anapplication, software, code, and/or other executable data instance)stored in storage device 4006.

Storage device 4006 may include one or more data storage media, devices,or configurations and may employ any type, form, and combination of datastorage media and/or device. For example, storage device 4006 mayinclude, but is not limited to, any combination of the non-volatilemedia and/or volatile media described herein. Electronic data, includingdata described herein, may be temporarily and/or permanently stored instorage device 4006. For example, data representative ofcomputer-executable instructions 4012 configured to direct processor4004 to perform any of the operations described herein may be storedwithin storage device 4006. In some examples, data may be arranged inone or more databases residing within storage device 4006.

I/O module 4008 may include one or more I/O modules configured toreceive user input and provide user output. I/O module 4008 may includeany hardware, firmware, software, or combination thereof supportive ofinput and output capabilities. For example, I/O module 4008 may includehardware and/or software for capturing user input, including, but notlimited to, a keyboard or keypad, a touchscreen component (e.g.,touchscreen display), a receiver (e.g., an RF or infrared receiver),motion sensors, and/or one or more input buttons.

I/O module 4008 may include one or more devices for presenting output toa user, including, but not limited to, a graphics engine, a display(e.g., a display screen), one or more output drivers (e.g., displaydrivers), one or more audio speakers, and one or more audio drivers. Incertain embodiments, I/O module 4008 is configured to provide graphicaldata to a display for presentation to a user. The graphical data may berepresentative of one or more graphical user interfaces and/or any othergraphical content as may serve a particular implementation.

FIG. 41 illustrates an exemplary method 4100 that may be performed bycontroller 104 and/or any implementation thereof. While FIG. 41illustrates exemplary operations according to one embodiment, otherembodiments may omit, add to, reorder, and/or modify any of theoperations shown in FIG. 41.

In operation 4102, a controller generates a single clock signal.Operation 4102 may be performed in any of the ways described herein.

In operation 4104, the controller interfaces with a plurality ofmagnetometers and a magnetic field generator included in a wearablesensor unit using the single clock signal. Operation 4104 may beperformed in any of the ways described herein.

FIG. 42 illustrates another exemplary method 4200 that may be performedby controller 104 and/or any implementation thereof. While FIG. 42illustrates exemplary operations according to one embodiment, otherembodiments may omit, add to, reorder, and/or modify any of theoperations shown in FIG. 42.

In operation 4202, a controller supplies a drive current to a lightsource included in a magnetometer. Operation 4202 may be performed inany of the ways described herein.

In operation 4204, the controller receives, at a differential signalmeasurement circuit, output current output by a signal photodetectorincluded the magnetometer. The output current is representative of anamount of light output by the light source in response to the drivecurrent. The differential signal measurement circuit is electricallyconnected to the signal photodetector by way of a twisted pair of wiresthat includes a first wire and a second wire. Operation 4204 may beperformed in any of the ways described herein.

In operation 4206, the controller measures, using the differentialsignal measurement circuit, the output current by measuring a differencebetween current going in to the differential signal measurement circuiton the first wire and current going out of the differential signalmeasurement circuit on the second wire. Operation 4206 may be performedin any of the ways described herein.

FIG. 43 illustrates another exemplary method 4300 that may be performedby controller 104 and/or any implementation thereof. While FIG. 43illustrates exemplary operations according to one embodiment, otherembodiments may omit, add to, reorder, and/or modify any of theoperations shown in FIG. 43.

In operation 4302, a controller supplies, by way of a first twisted paircable interface assembly included in a wearable sensor unit, a firstdrive current to a light source included in a magnetometer included inthe wearable sensor unit. Operation 4302 may be performed in any of theways described herein.

In operation 4304, the controller supplies, by way of a coaxial cableinterface assembly included in the wearable sensor unit, a second drivecurrent to a magnetic field generator included in the wearable sensorunit. Operation 4304 may be performed in any of the ways describedherein.

In operation 4306, the controller measures, by way of a second twistedpair cable interface assembly included in the wearable sensor unit,output current output by a signal photodetector included themagnetometer. The output current is representative of an amount of lightoutput by the light source in response to the first drive current.Operation 4306 may be performed in any of the ways described herein.

In the preceding description, various exemplary embodiments have beendescribed with reference to the accompanying drawings. It will, however,be evident that various modifications and changes may be made thereto,and additional embodiments may be implemented, without departing fromthe scope of the invention as set forth in the claims that follow. Forexample, certain features of one embodiment described herein may becombined with or substituted for features of another embodimentdescribed herein. The description and drawings are accordingly to beregarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A magnetic field measurement system comprising: awearable sensor unit comprising: a plurality of magnetometers, and amagnetic field generator configured to generate a compensation magneticfield configured to actively shield the magnetometers from ambientbackground magnetic fields; and a single controller configured togenerate a single clock signal and use the single clock signal to driveone or more components within the magnetometers.
 2. The magnetic fieldmeasurement system of claim 1, wherein the single controller is remotefrom the wearable sensor unit.
 3. The magnetic field measurement systemof claim 2, wherein the single controller is implemented by a computingdevice not configured to be worn by a user.
 4. The magnetic fieldmeasurement system of claim 2, wherein the single controller is includedin a wearable device configured to be worn by a user and separate fromthe wearable sensor unit.
 5. The magnetic field measurement system ofclaim 1, wherein the single controller is housed within a singlehousing.
 6. The magnetic field measurement system of claim 1, whereinthe single controller is included within the wearable sensor unit. 7.The magnetic field measurement system of claim 1, further comprising: anadditional wearable sensor unit comprising: an additional plurality ofmagnetometers, and an additional magnetic field generator configured togenerate an additional compensation magnetic field configured toactively shield the additional plurality of magnetometers from theambient background magnetic fields; wherein the single controller isfurther configured to interface with the additional plurality ofmagnetometers and the additional magnetic field generator.
 8. Themagnetic field measurement system of claim 7, wherein the singlecontroller is included within the wearable sensor unit.
 9. The magneticfield measurement system of claim 1, wherein the single controller isconfigured to interface with the magnetometers by way of one or moretwisted pair cables.
 10. The magnetic field measurement system of claim1, wherein the single controller is configured to interface with themagnetic field generator by way of one or more coaxial cables.
 11. Themagnetic field measurement system of claim 1, wherein: a magnetometerincluded in the plurality of magnetometers comprises a photodetector;and the single controller comprises a differential signal measurementcircuit configured to measure current output by the photodetector. 12.The magnetic field measurement system of claim 11, further comprising anunshielded cable configured to electrically connect the singlecontroller to the wearable sensor unit.
 13. The magnetic fieldmeasurement system of claim 11, wherein the photodetector comprises asignal photodetector configured to detect light output by a light sourcein the magnetometer after the light enters and exits a vapor cell of themagnetometer.
 14. The magnetic field measurement system of claim 11,wherein the photodetector comprises a monitor photodetector configuredto detect light output by a light source in the magnetometer before thelight enters a vapor cell of the magnetometer.
 15. The magnetic fieldmeasurement system of claim 1, wherein: a magnetometer included in theplurality of magnetometers comprises a vapor cell comprising an inputwindow and containing an alkali metal, and a light source configured tooutput light that passes through the input window and into the vaporcell along a transit path; and the wearable sensor unit furthercomprises a temperature control circuit external to the vapor cell andconfigured to create a temperature gradient within the vapor cell, thetemperature gradient configured to concentrate the alkali metal withinthe vapor cell away from the transit path of the light.
 16. The magneticfield measurement system of claim 1, wherein the single controller isconfigured to interface with one or more components within themagnetometer using alternating current.
 17. The magnetic fieldmeasurement system of claim 1, wherein: the magnetic field generatorcomprises: a plurality of conductive windings comprising a firstconductive winding arranged in a first plane, and a second conductivewinding arranged in a second plane that is substantially parallel to thefirst plane; the plurality of conductive windings are configured togenerate, when supplied with one or more drive currents by thecontroller, a first component of the compensation magnetic field, thefirst component of the compensation magnetic field configured toactively shield a magnetic field sensing region from the ambientbackground magnetic fields along a first axis that is substantiallyorthogonal to the first plane and the second plane; and themagnetometers are located within the magnetic field sensing region. 18.The magnetic field measurement system of claim 17, wherein the firstcomponent of the compensation magnetic field is configured to activelyshield the magnetic field sensing region by reducing or canceling afirst component of the ambient background magnetic field, the firstcomponent of the ambient background magnetic field being along the firstaxis.
 19. The magnetic field measurement system of claim 17, wherein themagnetic field generator further comprises: a first planar substrate; asecond planar substrate positioned opposite to the first planarsubstrate and separated from the first planar substrate by a gap, themagnetic field sensing region being located in the gap; a first wiringdisposed on the first planar substrate; a second wiring disposed on thesecond planar substrate; and one or more interconnects positionedbetween the first planar substrate and the second planar substrate andthat electrically connect the first wiring with the second wiring toform a first continuous electrical path, wherein the first continuouselectrical path forms a third conductive winding configured to generate,when supplied with a first additional drive current, a second componentof the compensation magnetic field configured to actively shield themagnetic field sensing region from the ambient background magnetic fieldalong a second axis that is substantially orthogonal to the first axis.20. The magnetic field measurement system of claim 19, wherein themagnetic field generator further comprises: a third wiring disposed onthe first planar substrate; and a fourth wiring disposed on the secondplanar substrate; wherein the one or more interconnects electricallyconnect the third wiring with the fourth wiring to form a secondcontinuous electrical path; and wherein the additional continuouselectrical path forms a fourth conductive winding configured togenerate, when supplied with a second additional drive current, a thirdcomponent of the compensation magnetic field configured to activelyshield the magnetic field sensing region from the ambient backgroundmagnetic fields along a third axis that is substantially orthogonal tothe first axis and the second axis.